As you will be aware, this is a relatively scarce model to find - especially in good condition. You may pay as much as you think is appropriate for one in the condition you mention. Restoration/repair is possible. They are hard to find.
The Thorens TD124 alone on which the BG3000 is based will cost at least 800 - 1000 € minimum these days. I've seen some sell for over 2000 € even unrestored. As a guide, this is mine which was fully restored by Classic Audio and cabinet/plinth made in Oak to order and a new TT cover (not shown) and cost around 1900 € including delivery and a restored/retipped SP14 cartridge (+2 spares actually), with calibration and restoration booklet and certificates. It is flawless and sounds wonderful.

It's worth every single Centime.
What is the price of the one you have found? Is it a pickup/cartridge problem, tonearm wiring or just the stylus?
Dave.