125 cc skyteam repairs ?

Skyteam ST125SM

I am writing to your hoping that someone can help me with a huge problem I have. My husband has recently purchased the above bike from eBay from what we believe to be a reputable seller. The bike was originally purchased in Leeds from dealership and then has been sat in a garage for 18 moths as the owner bought a car and never used it. It only has 650 miles on the clock and was sin good condition when we purchased it for £750.00. After collecting the bike o the 1st ride out something has snapped on the wheel bearing at the back and the wheel now wobbles. It appears to be a big problem as we have had a bike mechanic look at it who says it will cost more to repair than we paid for it. I simply can’t believe this and after spending over £1300 including insurance and equipments im so disappointed I don’t know what to do. I found your site on Google and wondered desperately if you could offer me and advise on how easy these bikes are to repair and costs of repairs as the mechanic was very negative but not a specialist with these types of bikes.
I would greatly appreciate anything you can do to help and I may be able to provide more details of what parts etc are required when I speak to the mechanic. I simply can’t believe that the bike is worthless as it’s in very good condition, relatively new and seems to have faulty part. Yours hopefully. Mrs Anna Oliver