My latest watch was a £75 purchase from eBay, a Seiko SKX031. It’s an automatic, which is great for people (like me) who are too lazy to change the battery and consequently have a pile of stopped watches sitting on the side.
I got the strap adjusted at a great little jeweller’s in Shaftesbury Avenue, Mr. Chan’s. Mr Chan himself is very knowledgeable about watches, and identified my 1970 Rolex Airking as I walked in (he even pointed out it didn’t have its original strap)!