While Sony MIJ hasn't been available in 100-packs, it's been ubiquitous in the 50-packs, which, as you might have noticed, are also on sale. Unfortunately, MIJ media has been slowly disappearing from the market, so finding them now will be much more difficult.
Office Depot will also have Sony media on sale next week, only $12.99 for a 50-pack, so you can PM them at Staples and knock the price down a couple more bucks. OD rarely has MIJs, although they did send out some 50% off coupons for Sony media, so at least the MITs will be cheap.
Lastly, you can always use the Staples or Office Depot ad to get some 8x +R MIJ Sony media at Sears with a price match. Those are TYs.