I don't shoot much video.

When I got a standard-def mini-DV camcorder, my dad told me keep the original tapes and just buy new tapes to record new stuff, since the tapes were cheap compared to the drive space needed to hold a tape of data. It's like 2GB every 10 minutes or something for RAW DV data, so a tape would hold 12GB on a 60 minute tape. That works out to 85 DV tapes per terabyte. With the price of harddrives these days being like $80/TB (I know it varies wildly, and you'll find this value to be wrong). Using DV tapes is only viable if I can get tapes for about a $1 each, which I don't think I can.

Only you know if you're okay with reduced quality, and once you figure out the space requirements for the quality you want you can determine what's the most cost effective storage (hard drives, writable blurays, tape backup system, etc.).

I don't have a suggestion on what you can use to bulk reduce quality of your data before archiving.