With WMA lossless the bit rate depends on the music. Microsoft advertises 470-940 kbps, in other terms 200-400 MB per disc or about 1:2-1:4 compression ratio compared to the raw data.
I don't have a BS5, but thanks to fishta's idea, I've finally started to rip my CD collection by feeding them to my laptop while reading the morning paper (will take a few days more). I have now ripped 112 discs and they consume 32 GB on the disc which is a little less than 300 MB per record.
The process works pretty well nowadays - I have only spotted one record which didn't get at least decently correct tagging. Some records are missing the cover art, but those are mainly more esoteric Finnish albums. WMA Lossless is a safe format in that you can convert it to other formats even with free tools. I'll eventually go to FLAC as I very much prefer free multiplatform choices, but I didn't have the energy to think of how to do that directly with this ease.
Now I only need to think of what I'm going to do with all those bits. Much of my CD collection, mostly acquired 15-20 years ago, is such utter sh1te that I can only hope I didn't pay normal prices for them...
BTW, this Vista laptop of mine starts the ripping process automatically after just inserting a disc, even if Media Player is not running. The key to this might be in the autoplay settings, but having MP start automatically after boot is probably just as good a solution.