Your Mixmaster:
Is a Model MMA or MMB, known to collectors as a "Plasticmaster," because its outer shell is plastic instead of the cast metal of earlier models.
MM-series mixers are good mixers. However, because they're both recent and very plentiful, they're not economical to repair; you can find an identical one on eBay or at thrift stores or at estate or yard sales cheaply.
The man who declined to work on yours was being honest; the cost-to-repair would be higher than replacement cost.
Again, these are good mixers - I am not trying to be snarky about them. It's just a cost factor. Sunbeam sold literally millions of these, so there's a new one out there waiting for you, cheap. The fact that yours is Harvest Gold makes it even cheaper to replace the mixer; that is not a color many people look for nowadays.
I hope this helps.