The difference between the budget kits and the high end kits usually comes down to fit/finish, materials used, ease of maintenance/tuning and support.

The high end kits use carbon fiber or aluminum for chassis and shock towers where the budget kits will use FRP. The quality of the plastics are usually better on the high end kits.

The budget kits can be very competitive at the club level in the right hands. Most of the time build, maintenance and setup can really make or break a car's handling, regardless of how much you spent on the car. A properly built/maintained/setup budget car will run circles around a poorly built/maintained/setup high end car.

On the other hand, there can be a lot of frustrations with the budget cars. Sometimes the instructions leave a lot to be desired. The fit of parts can be very frustrating during the build. And I do think there is a durability difference as well. If you are racing outdoors without walls/pipes close to the track, durability is probably not an issue, but in tight indoor carpet layouts, you might see a difference in durability.

These are only my opinions and they are worth exactly what you paid for them!! :-)