If you're confident enough in your own technical skills, then I say go for it, OP. But if you aren't that handy in the first place, then you're better off buying a new PS3 rather than messing with someone else's system.
The disc drive is probably the easiest repair out of the entire system, as I've known a few people who repaired/replaced theirs.
Thing is, the most common problem with the disc drive is the SAME issue the PS2's had at times: dirty lenses.
A little rubbing alcohol, a q-tip, some time and patience and you could have a great working system.
My one ex buddy from CAG/PSN even went so far as to take apart the lens and clean the mirrors the beam bounces off of and that made his 60 gb PS3 read like new again.