TW, the previous poster, wrote a little pamphlet called The Bermuda Bible. Search the Internet for it and follow it.

Assuming you have a high pH soil, here's what you're doing wrong. You are blaming your problems on cheap grass. Well, the grass may have been relatively inexpensive but the grass is not cheap. The bermuda seed you are planning to buy is cheap grass. The sod that was put down is an improved hybrid bermuda that does not produce seed heads. When you are taking proper care of it, it looks amazing.

Cure for hard soil
Buy the generic brand of baby shampoo at Wally's. Measure your lawn. The app rate is 3 ounces per 1,000 square feet. If your lawn is 4,000 square feet, you need 12 ounces of soap. Put that amount into your hose end sprayer and set the dial to 3 ounces per gallon. Spray that on your lawn until it is gone. Then irrigate the lawn. Apply a full inch of water. Since your soil is currently hard, I would expect the water to run off after about a minute. As soon as you see runoff, stop watering and wait for 15-30 minutes. Then continue watering until you see runoff again or until you get a full inch of water down. The irrigation will carry the soap down into the soil where it will soften your soil. Actually all the soap does is help maintain a more even moisture level deeper into the soil. Then next week water without the soap. The week after that, repeat the soap and water again. That should do it for your hard soil. Soil is supposed to be hard when dry and soft when moist. And it should absorb water like a sponge - meaning it should run off at first and then suck it up like a, well, sponge.

Your builder didn't do anything to the soil before he planted grass.
Cry me a river. He didn't do anything for the rest of the lawns in your neighborhood either and they're doing fine. You don't have to do anything to the soil before you plant sod. You're supposed to water (properly), mow (properly), and fertilizer (properly) after the sod is down. For bermuda you should water it no more frequently than once a month in the cool season and work your way up to every 7 days when the temps approach 100 degrees. If you are in soft sand with an arid breeze blowing off the mountains, then you can water every 5 days in the heat of summer. When you water go for a full inch every time. If you get an inch of rain then you don't need to water. If you get 1/3 inch of rain, then you need to add 2/3 of irrigation.

Bermuda needs to be mowed at least every week and preferably 2x per week. Mow it at 1.5 inches or lower. If that setting scalps the lawn, then you have other issues which can be fixed.

Bermuda needs to be fertilized with lots of nitrogen every month to look its best. Forget about weed n feed products. They don't do what you think they will do anyway - waste of money. Use a real man's fertilizer and a real man's weed killer. Don't fertilize in the spring until you mow real grass (not weeds) for the second time. Fertilizing before that time is a waste of money. Why? Because fertilizer works through the roots. If you don't have grass growing, the roots aren't taking up nutrients. Once you get grass growing, then hit it with high N fert every month until about Thanksgiving. NOTE TO OTHER READERS - THIS IS ONLY FOR BERMUDA.

Hope this helps. Read the Bermuda Bible.

Also, what do I do about the bahia? i hear it is almost impossible to kill.

Mowing - how often, what height?
Fertilizing - timing, how often, what products?
watering - how often, how much water each time?

Find your nearest John Deer LESCO Landscape dealer and get a product called Riverdale Manor. Takes two applications from a hose end sprayer, six to eight weeks apart. It is a professional product golf course superintendents use an dis rather expensive, but not controlled and can be bought and used by the public.

FWIW again I say assuming your soil PH is above 6.0, Bermuda grass is the toughest grass there is and will perform better than any of the other warm season grasses with your conditions. If your PH is below 6.0 Centiweed is your only option as it is the only warm season grass that can grow in low PH (acid) soils. So get your soil PH tested and go from there.

No such thing as cheap Bermuda sod. 80% of the Bermuda Sod sold is either Tifway-I (aka 419) or the improved version Tifway-II. It is one of the finest quality Bermuda sod money can buy. It just happens to be low cost. Not because it is low quality, but because it is so plentiful and has been in commercial production for 52 years.

Any sod farm that sells Bermuda sod has Tifway 419. will be their largest seller and the golden goose of the farm. It will also be the least expensive of the Bermuda varieties.

Only other variety I would recommend over Tifway-I or Tifway-II is TifSport. At my former sod farm in TX we sell Tifway-II for $75/pallet, and TifSport for $105/pallet.