I don't know much about wrenching but I can offer you a simple formula to come up w a buying number.
You say that $3500 should get you a bike in so so condition, well you need to figure out that: if you pay $1000 you can only spend $2500 to break even.
This bikes are great when maintained bc once things go south replacement parts are expensive.
Btw a 2002 1150 should go for more than $4500 in ok condition.
Good luck, play it safe and under pay so you can protect yourself.
"The Only Easy Day Was Yesterday"