Just to give everyone a feel for price here are some numbers from the UK.
Jamun Mygale SJ11 used post race season will more than likely fetch $28,000 minus dampers, engine, and data logging equipment. A Ray GRS07 Kent converted with everything will run $23,500 minus data. Newer Van Diemens are hard to come by but a RF00 is for sale right now at $17,800. These cars would come fairly close to stock which means there would be some time and money spent upgrading to lighter components. Add in a conversion to Honda power and $50k would more than likely not get you what you want. However if you bought an existing Kent engined car like the RF00 then you would have about 35k invested after required upgrades to make it competitive. I'm racing over here and I have about $6k in upgrades left to do which will lighten the car up by about 30-35 pounds. Needless to say the cars here don't have some of the nice upgrades you all take for granted.