Feel the area with your hand where it has peeled under the tires. My guess is it is a smooth as glass. If so, that is one of your problems. Whatever product you decide to put down it needs to be roughed up so the product will stick. Shotblasting being the best, mechanical grinding being next, and acid etching trailing. No matter what prep method you choose the idea is the same. Once you think you are done feel the floor, it should be like medium grit sandpaper.
Something that does not get metioned much on this forum is that you can sandblast also. It is REALLY messy, but if cost is the main objective then it should be considered. It is rleatively inexpensive but should yield the objective of roughing up the concrete. Just make sure it is dust free when you start the coating.
If you are using a thin product it will most likely not end up with a smooth finish if you get a good prep. By thin I mean water based or something less that 100% solids.
I don't like to suggest products as there a just way too many out there. If you have not read "the truth about epoxies" you might get some more data there about selecting a good product.
A urethane topcoat will make all your work last that much longer. Yup it cost a little money, but it will look better and last longer so in the long haul you will save money. If you have to do it again in 2 years how much money have you saved????
You can only do it so cheap before there is no chance of a decent finished product.