I’ve bought 25 packs of Office Depot brand RW (mostly -RW for my DVD Recorder) when they go on sale for $8, and I have recently seen Sony 25 packs for $10 which is a good price as well. I’ve used Infodisc, Ritek, and RICOHJPN RW media and all have performed fine for me under limited amounts of rewrites - all 3 of those would probably be considered only ‘average’ in terms of RW media, but I’ve not had any glaring issues with them. Verbatim MKM is supposed to be among the best RW media although I haven’t personally used any in a long time. I have not done a lot of testing to see how my Ritek/RICOHJPN/Infodisc under a large amount of rewrites though and it’s not uncommon to hear of people having problems with RW media after only a few rewrites depending on the media code, burner, etc. Having said that, I know some people have rewritten discs dozens of times without problems so it is somewhat unpredictable, and I’ve had discs that I’ve written about 15, maybe 20 times without issue.
You may want to also look into DVD-RAM for frequent backups. Although the 5x DVD-RAM discs perform a little slower than 4x RW media, they are a more reliable/stable format. They perform much like a Hard Drive without having to use risky packet-writing programs that are required for similar functionality in RW media, so they may be more convenient to use depending on how you plan on doing your backups. They cost quite a bit more than even RW media but if you don’t need many then they aren’t too expensive and they last far longer than RW media, which can sometimes develop problems after only a few rewrites in some cases. DVD-RAM media is supposedly capable of 1,000-10,000 rewrites. You can order them direct from Panasonic for $8 shipped for three 5x discs, or about $1.20-$2 for the 3x discs, depending on how many you order. Of course you may or may not have a drive supporting the format.