Does your track have an on-site shop? If so I would check to see what brands they support and limit your selection to only those brands. I'd hit up the locals on race day to see who's looking to sell their (no more than 1 release old chassis) most rollers should go for around $150, great way to stretch your dollar.

In my area the most popular 2WD brands on turf are XRay and Associated.

I prefer to run 4WD classes because they get almost double the lifespan of tire wear on the turf track in my area making 4WD significantly more economical over the long haul