I posted against another question last month - It is best to get one with a hot gas defrost as this will enable it to work well when it gets cold. A good unit we bought was this one (no affifliation) Dry-it-out
It is a bit fiddly to get a pipe to drain it into the sink but thin surgical hose worked OK.
B&Q seconded (or thirded???)
Ran one for the last 3 years until we moved to a place warm enough not to need one.
Had it on 24/7 with the humidity setting on about 5 and it kept our Dehler 37 in perfect condition used with 2 135 watt tube heaters.
Didn't reckon £25 a year was bad really......it's still in perfect working order too.
Got a dinky little one in a sale from Woolworths last week for £15! Might have some more left if you're lucky. Figure it's good enough for the smaller forward cabin on a timer on a shelf - it doesn't really get too damp in there anyhow.