I'd agree the seller is rather..let's say..optimistic with the asking price. 450 USD seems plenty, in my market at least. No idea what the market is like in CA.

Passing thought..having just bought and sold(too small for me) a 1990 Trek 970 and comparing the 970 to my GF's 1991 Trek 750 Multitrack.. The 970 and 750 looked like same frame. The seatpost cluster on the 520 photos here look identical to the 1991 750 and 1990 970. I compared the geometry of the 520, 750, and 970 a while back and if memory serves..they were basically identical in the 1990-1993 range. I didn't check the tubing though. After 1993 the 970 top tube got longer, but in the 90-93 range the top tube of a 20 inch frame(the size typically for a person that rides a 56cm road frame..like me..and you apparently) was 57.5cm. The 1990 520 (21 inch frame, as the spec manual lists it) has a 56.5cm top tube.

The short version of the above..if you're having a hard time finding a 520, you could consider a 750, 790, 950, or 970 from the 1990-1993 range and do a drop bar conversion into a touring bike. These bikes will run $100-$250USD range. I saw a converted 970 this morning on CL..with a 30.5" standover height..it's a 20 inch frame. Looks t be a 1990 bike.
https://minneapolis.craigslist.org/h...145363931.html