For that budget you'll probably get a good example with an Ittok arm. Preferably look for one that is post 1985 with the stronger corner bracing.
They start from around £650-700 in good condition with a Valhalla power supply and an LV11 Ittok. The later Ittok LV111 is even better (and more pricey!) but there's not that many around.
For £900 you may possibly get a Lingo (external) PSU thrown in as well. You might even find one with an Ekos arm, rather than the Ittok, if you're very lucky, but avoid the earlier Ekos Mk1, which was arguably not as good as the later Ittoks.
The Ekos Mk2 came in around 1992 and was a marked improvement over the early ones and well worth getting if you can find one for the price.
You will see LP12s on sale with Cirkus bearings and earlier non-Cirkus bearings. Its difficult to say which is better, they do sound different but its a matter of personal taste which one you might prefer.
Another 'upgrade' you may see in adverts is the Trampolin base. It seems most people prefer LP12s w/o this mod, others say its OK but no big-deal.
If you're buying privately or from a non-Linn authorised dealer its well worth getting the deck/arm checked out by an authorised dealer if you can before commiting yourself. As well as the main bearing, there are potential problems with worn/sticky arm bearings and an arm with sticky bearings is worth about square root of FA, so be warned! If you want to gen-up some more on the LP12, you'll find a wealth of info
here and elsewhere. Happy hunting

David