Many dealerships don't have recent experience with the older tractors like your 300 and it might cost quite a bit for the younger technicians there to learn at your expense.
You can get the CD version of the technical manual for your tractor from Deere for far less than an hour of the dealer's shop time -- and getting it fixed yourself can be quite gratifying. The PTO not engaging reliably is most likely an air gap issue, there are many threads on this forum about making that adjustment. Here is a small excerpt from a later model tractor, but the method is almost identical
The Kohler engine in your tractor is a real solid performer when running right, and you can get the manuals for free download at:
This manual is about 6 MB, so I could e-mail you a copy if you have trouble finding it on-line. Here is a table from that publication that shows starting places for each carburetor size/type.
I currently have a Wheel Horse C-145 hydro tractor with the 14 horse Kohler that runs pretty well and am selling it, the tiller and mowing deck for $450.
You will find there is a logical limit as to what you would/should pay a shop for engine/carb work on one of these older tractors if you don't feel you can do it yourself...but you might be surprised at how simple these old machines really are!