If bowl turning is your thing then you can sometimes find a Union Graduate on eBay for about £300. It will probably just be the main body of the lathe and maybe the outboard side. Many seem to be modified to a Disc Sander as they had a large outboard capacity and can go quite slow. I purchased my graduate as the main body, outboard bed and that was about it. I since had a short bed made for the inboard side and it has a nice bowl lathe with a 24" capacity, I hope to upgrade it one day to have a larger variable speed motor but may have to sell it to make room for the many things that come with having a small child. We shall see!
The metalwork that I had done cost about £200, which was ontop of the £200 for the lathe. But I sold my old Axminster AWVSL1000 for £400 so I feel like it was worth it. I had a very heavy bed added as well as a Y shaped base which has wheels which can be jacked up for when I don't need to move it. When I use it I simply lower the feet and the wheels don't make contact with the floor and I have a solid base for turning.
They are decent lathes for modification because they are solid and have some useful flat faces and a large cavity inside for fitting a new motor. As far as I know, there aren't many options for someone who wants a lathe they can refurbish and upgrade over time.