If you want one now then you can pick one up for only $30 or so. But if you dont need it now and can wait about 6 more months or so until DVD-RW come down in price then thats a way to go. IMO if you want one now, then you might as well get a cheap LITEON or LG.
If you look for a bit, you can usually pick up a 4x burner for around $70 after a rebate. I purchased an 8X NEC burner for $100 from www.newegg.com . Making backups of your DVD's is very much worth it, especially after the kids destroy your "Finding Nemo" dvd....twice.