Cat amongst the pidgeons
An 883 Sportster.
Top end of your budget, won't green lane(very well) and you'll have to plaster it in protective spray to stop it rotting.
100% reliable, cheap and easy to maintain, cheap tyres, belt drive(never needs adjusting) fun to ride(honest), easy to get parts not that you'll need any. Get more back in ten years than you'll pay for it.