Slap-together carpentry is so easy, I would always recommend building your own: trawl charity shops(some specialise in furniture), church sales, root through skips, watch out for street-dumped furniture etc.
Decide how high you want your surface: I like about 750mm, which is the height of standard kitchen units without legs, so have a look at Ikea's system, or others, for the base unit(s), legs etc.
Check out timber yards for worktop offcuts: a normal 40mm kitchen worktop is 3metres long, so if someone wants a shorter one, the yard will have cheap remains, easily big enough for a hobby desk.
I recommend a metal office filing cabinet with lots of shallow drawers: mine has 11 60mm deep drawers, which makes rooting for that tool or spare part very easy.
Plan your lighting too: I like one anglepoise magnifier fluorescent, some prefer 2 anglepoises, or poseable spots on shelves above.
Oh, and a dedicated coffee mug spot helps stop you accidentally drinking your paint water!