I've mentioned the SL1200 as you can get these for a reasonable price on Ebay, although shop around for a deal for the new version too. Maybe worth checking if there are any differences build-wise or in the internals on the new models against the old ones. Either way, assuming there's no big differences, Audio Origami and Origin do customised Rega arms (I'm not sure about the others that you could put on to be honest or the pros and cons of those), but the price increases accordingly. I think we're talking around the £400 figure or thereabouts.
If you buy secondhand, but get a good condition model, you can then get the cooking RB250 (easier to mod than the RB300) for about £130 or so (plus the cost of the work to install it on top) and bung on a good cartridge. If funds are a little tight, you can always get the new deck and a cartridge. Either way, they are superbly built decks and - like the LP12 - haven't been around since the 1970s for nothing!
Incidentally and depending on if I ever find it, there was a thread on a forum somewhere by a chap in Germany who'd done the mother of ALL mods on a knackered old Technics deck. I mean, this was a mouthwatering, jaw dropping, stunning piece of work. I'll trawl the pages again, if only to see it for myself once more.