It depends what you buy, if your after a mini, you pick one up on here for £100-£150, the price of a new one is £300, your unlikey to need to spend £100-£150 fixing it if its a duff (unless a frames bent or something out of the ordinary). If you pick up an axe the same thing applies, £400 ish new, £200-£250 second hand, but solenoids and board for axe/mind are cheaper than the likes of planet eclipse in my experience, think i got a solenoid once for about £20 (a while ago), baught a new baord ( the updated shockwave board) not so long ago for about same price.
If you buy something new you get the safety of a warranty, but its still hassle if it croaks on you, youve got to post the marker off generally which isnt cheap. If you buy from someone on here generally if you have a problem its resolved, lots of us here to lend a hand. But if your buying second hand it opens a lot more options of marker. X