informal = cheap, Pat has a good approach. It will get expensive if you have to keep buying them. Informal also means you don't have to worry about measuring EXACTLY 30Ft, just get them close. You can find closeout sales on party streamers if you look long enough...

Lately, I haven't been cutting to length at all. I cut the party streamer in half with the band saw and just bring the rolls to the field, and then pull out enought to were the length "looks about right".