I would build terraces myself, using concrete wall stones. Home Depot and similar stores sell a kind of stone called a "Windsor block," which have a little lip on the back, so that they won't slide when you stack them. They're designed to build retaining walls, and they don't require mortar. They're not designed to make 90-degree corners, but they make gentle curves very nicely. They are extremely easy to use.

Start at the lowest corner, dig out the grass (or whatever), and lay a stone. Try to get it level. Continue along the bottom edge, keeping the stones level. If you get to the point where the next stone would be completely buried, move up a level and keep going.

When you get all the way across, stack them up until you have a bed as high as you like -- 2, 3, or 4 stones, I'd say, depending on your preference, and the steepness of your slope, and depending on whether you have any interest in adding more dirt from an outside source. While doing this, curve the edges around so that the wall continues backwards to the back part of the first terrace (decide how far back you want it to go). "Cut and fill" the dirt on the slope to level out your first terrace. Add additional dirt if you need it, then build your next wall. Repeat as necessary until you run out of slope.

It's not too bad, really!

I'm in So Cal and most all of my garden now WAS on a slope. We built a retaining wall at the lowest point and leveled off a great portion of it and backfilled with a good soil/manure mix. If your soil is already nice and not rocky, I'd terrace it. I'd actually use the landscaping timbers at Home Depot if you are looking to keep costs low. They are about $3 each and 8 feet long. I placed a link to a terraced area that used the timbers I referenced.

Here is a link that might be useful: terraced garden with landscape timbers

Does the lower half of the garden level off?

If you use the blocks, I have laid thousands of them, you absolutely MUST lay a buried, or partially buried, row.
Depending on your soil, you may be able to just level it with native soil but it would be much wiser to put in a few inches of sand to level the bottom blocks.

How much higher is the high end from the lower?
Which way is the slope the long way or the short way?

I raised the lower end of my one garden by eight inches by putting in old railroad ties from Menards.
I protected my one rose garden from winds by putting a tie wall three high at the North short end but I am going to drop it down to two high.
The entire garden has ties one level high with stair-case type rising to the high end.

Whether you use landscape timber or railroad ties, buy twelve to sixteen inch spikes to fasten them together.
There are long, I have used up to twelve inch, screws that are easier to install but cost more.

A heavy-duty 3/4 inch drive drill makes putting the screws in easier.
I have driven spikes in with a sledge but it takes practice as the most common error is not hitting the spike square and ruining the hammer handle.

The base is VERY, VERY important or the wall will collapse or as happened to a person I worked with wash out from underneath in a heavy rain because they were in a hurry.

I half buried layer of ties for the vegetalbe garden as it frop apprx six inches from one end and is not not level but does not wash in a heavy rain anymore.

RpR_ has good advice about burying and/or using an underlayment of the blocks, but I've had loads of success just using my native soil, and a minimum of burying. My current wall is only a few years old, but it's made it through a few Winters, and is doing great.

You're going to have to consider your conditions. Even with burying and/or underlayments, though, the wall stones are still super-easy to use.

You may be able to adjust how you plant and work with the less than level areas without terracing. Work the beds to leave ridges parallel to the direction of the slope much like farmers use contour plowing. Work up only the areas you are going to plant right away. Mulch the areas with leaves, straw, etc. to reduce the soil disturbance during rainstorms. Leave strips (maybe walkways) untilled with grass or other soil holding roots in place.

Do you get heavy intense rainstorms or gentle rains? If you see lots of intense storms during times your soil is not protected with the roots of growing plants and mulch, the planting modifications may not be enough and you will need to use other methods.

In areas with the greatest slope you may need to go with more drastic erosion control. Perhaps they can be graded into a longer, gentler slope with interspersed level areas. I'd try the low imput methods first and watch closely to see if the added work and expense of terracing is necessary. Also see how the group gardening works for all of you, consider how long you plan to use the area, think about not using the section with the greatest slope, before spending hundreds or thousands on materials.

a 1 to 5% slope seems easy to deal with. I would not even buy those expensive stones, and instead use cheaper cinder blocks for terracing. If need be, salvaged metal pipes can be cut to produce a stake to further stabilize the block.

I love my terraced hillside veggie garden. It's beautiful and the drainage is awesome. Two weeks ago, I was able to do a little digging two days after getting 5 inches of rain.

Start at the bottom of the slope, and use boards held in place with rebar stakes (pounded in flush with the tops of the boards) to structure your beds. As you do so, you level off the permanent pathways, which gives you some fill dirt. Unplaned boards from a lumber yard are cheap, and even untreated they last several years, then easy to replace.

There is a Hillside Garden forum here with some ideas, too.

Here is a link that might be useful: pics of my hillside garden

Another vote for building terraced beds. Lots of sloped gardens in my neck of the woods given the Ozark Hills and terraced beds are ideal.

Dave

Here is a link that might be useful: pics of terraced garden beds