Our builder car is a base 4 door 2.2L 5 speed. Nothing mechanical has been touched other than timing belt and oil pump reseal a few months back when I was daily driving the car. Addition of a roll cage and we had it listed at $4k and had quite a few people interested. Family member wants to pick it up so selling it to him for $3.5k. This allows you to build the car up to the spec you want over time at a minimal initial investment. If you want it ready to rally, plan on more of the 8-12k range.
We also have spec E36 Group 2 options. Builder 92 325i is sitting here acting as my daily driver for now. That one is going to be more like $11-12k ready to rally. That'll be more of a car than an Open Light car however with RWD, LSD, and 220 hp.