In reply to KennyG:
Yep, a cheapish (i.e. not that skinny) 50m rope seems the affordable option - it'll cope with indoor use, be long enough for outdoirs, and not be too expensive to THROW AWAY if damaged (or cut ends off if end damage). Just check your local sport crag is not 23m or bigger...and when outdoors, ALWAYS make sure the tail end of the rope is tied to rope bag or another climber - stops end running thru belay and dropping folk.
Other poster is right, you may need longer rope for abroad, 60 or 70 depending where. As a 50m fan (30m at my locall indoor wall), I find 70m a PITA tho.