And here. A Planar 2 is a great inexpensive TT, but adding a cartridge (the Rega ND3 is ideal) will take it quite a bit over your £500 budget. Pro-Jects are decent. For your budget, I'd steer clear of real vintage items. Any suspended sub-chassis designs, such as Linn, that you can get for £500 are almost certainly going to need you to spend money to bring them up to snuff.
However, something like a used but fairly recent Planar 2 or 3 (or Pro-Ject equivalent) would fit the bill and come in around budget. At that level, people upgrade quite quickly, so you can pick things up that aren't too old or heavily used.
I'm a Rega fan because they're made in England, spares/parts are readily available and they sound excellent for the price. They're also a nice to deal with smaller independent company and not part of a faceless corporation, which is important to me.
Re siting a TT, unless your floors are flimsy and you jump around whilst listening to music, you'll be fine and won't need trick isolation devices. Purpose built hi-fi racks and shelving from the likes of Atacama are ridiculously over-priced. High mass shelves are often counter-productive, because they store low frequency resonance. A good inexpensive hack is to buy a laminated bamboo cutting board (they're light, rigid and non-resonant) of suitable size and add adjustable spikes at each corner so it can be levelled. Put it on top of your sideboard or wherever and stand the TT on it. I've done that with my Planar 6 and it works very well. I can tap the rack it sits on firmly whilst a record is playing and no sound comes through my speakers.