The E28 is a the first generation with all the electronic goodies, and is a semi advanced car. Like the 2002, those cars are so simple that most of the work i can do myself. Strip a car down to just a shell i can do. Then send the shell off for bodywork and spray. Reassembly i would do myself. That keeps the cost down, and give me the fun part of the restoration
E28 is a bigger and more complicated car. If you are to set it away for others to do the whole job, it will be costly. It all depends of how much you can do yourself. Look at Malaycooper, the job that he has done himself on his 735i has saved him thousands. I am afraid that keeping a classic require anyone (except the filthy rich) to get their hands dirty.