Strips? Are you talking about precut foam or R-board...or the precut batts of fiberglass?
The foam & R-board have both gone up considerably as of late, & aren't likely to go down for the foreseeable future. If you have a Menards in your area, they usually run big sales on base construction materials (i.e. lumber, plywood & OSB, insulation, roofing, etc.) in early spring- mid-March, I think.
Fiberglass insulation is on sale at a couple of places right now, and I know Menards has a current rebate on it.
Did mine over last year due to a leak upstairs. Went with R19 rolls and cut to length. I think they were about $23 for a 30 foot roll at HD. Also went with OSB instead of drywall. After tearing out all the soaking wet drywall and insulation I decided to go with OSB. Biggest pain in the ass mess trying to rip out soaking wet pieces of drywall. If it ever happens again, just unscrew the damaged OSB sheets and toss out. I'll be doing the other side this year all OSB too.
Couple pics -