Bonus with sprayfoam; if you go with close cell foam of sufficient dept (1.75-2" I believe) it also acts as a vapor barrier...
I don't know if that's a requirement where you're at, but up here in Canada, it is - and the labour savings in not having to hang and seal the poly vapor barrier helps offset the increased cost of the spray foam...
As for DIY foam kits, they are out there, Tiger Foam (»
www.tigerfoam.com/) is the one I'm most familiar with - comes in two tanks, with a set of hoses and applicator - works well, when you get the hang of it - but it's not cheap... If you have a substantial amount of foaming to do, it may be cost-neutral or even a better value, to bring in pro's. Worth a call, anyways...