Pictures of the side yards would help to generate ideas. Are you thinking of a border garden with some low maintenance plants? I would suggest also lots of mulch to keep the weeds down and also retain moisture for the plants. Are you familiar with the practice of sheet mulching? Here is an example: my border garden, sheet mulched, with a mixture of native and non-native plants. My trash cans go about where I was standing when I took the picture.

Thank you for the reply. I didn't take pictures of the yard. But it's just a 6ft wide area long the side of my house. Your sideyard looks good. I am also thinking of a concrete path (about 80-90ft) in the middle with either mulch or gravel on both sides. But not sure how much would the path cost. Also does mulch provide a good weed barrier. How often do you need to replace the mulch. Which one has the least maintenance, mulch or gravel?

It sounds like you are looking to replace plantings completely and leaving an area strictly as a passageway?
I'd go with gravel rather than concrete. Installed over a properly prepared "bed" (excavated slightly, filled with stone dust or crushed stone, compacted) a gravel walk will be permeable, unlike concrete, which might create a water run-off issue. Rather that fill the entire area with hardscape, how about a gravel path about 3-4 ft. wide (depending on the width you need for your mower, 4 is usually more convenient) and planting a suitable ground cover on the sides? You will get some weeds in the gravel eventually, but if you blow off the path to keep it free of organic material, it will be less hospitable to weed seedlings. A bit of roundup, if absolutely necessary, can be used to zap any that do come up if you can't pull them.

Hi again. Sheet mulching provides a good weed barrier. I cut the grass short and used a shovel to dig out a shallow perimeter. Then I laid down cardboard over the short grass and secured on the perimeter shallow trench by baseball-sized stones. Then 4-6 inches of mulch on top. In a year, the cardboard has decomposed, and your grass is gone. I mulch twice a year, but you could get away with once a year. The wood chips are free from your local tree companies and used cardboard is free, too. You may get a few weeds with mulch, but not many, and they are easy to pull up. I like sheet mulching over gravel because the materials are free, and it's easy to turn into a border garden on either side of your path when the finances free up. I did install a scree garden on one side of my house, to remind me of fond memories hiking. Scree or gravel is supposed to discourage pests (such as carpenter ants). Here is a picture that shows the scree garden with a curvy border and I put cardboard underneath. As noted above, concrete does not allow the rain to seep into the ground, while gravel does.

The least expensive idea I know is used carpeting. I've seen it used right-side up and upside down. I've seen it installed poorly (laid down with no preparation) so it's roughshod looking, and I've seen it installed where the surface has been smoothed over quite well. In some cases, I've seen it right-side up with sand embedded in the surface so it was actually hard to tell that there was carpet. It seemed like packed, smooth, very firm sand. I have never used it, but it seems to me that the end product is highly dependent on the preparation and care of installation. Sand as a base seems key. Since carpet installers are removing large amounts every day, it's readily available and the price is right.