Unless you do the work yourself, you will NOT get a C36 engine & tranny to work in your 300E for $10K. Budget closer to $15-20K. I kid you not, esp. since I basically did the same with our the wagon, but I did all the electrical research and wiring myself.
If your car was a 93-95 E320, then you could just drop in a 1995-1996 C36 engine & tranny.
An easier drop-in would be an EARLY 104 engine that used CIS instead HFM.
Again, you'd get more performance selling your car, and purchasing a 400E (low teens). Drop a 3.07 or 2.82 diff in a 400E and you have 80% 500E performance.
1988 360TE AMG