I went cheap. These worked great, batts lasted all week. In fact they still work now. Need to remove the batts and clean the box when home but they pasted the playa test.

These are super cheap and almost too bright to look at. Bought a bunch to sew inside light colored clothing and wrap on bike. Am very happy with the results.

http://www.amazon.com/gp/product/B004DYV2RE/ref=oh_details_o07_s00_i00?ie=UTF8&psc=1

These are even cheaper, not so retina frying, and good for wearing on outside of costume.

http://www.amazon.com/gp/product/B00IJ46DUU/ref=oh_details_o07_s00_i00?ie=UTF8&psc=1

I'm so over the last minute, impulse purchased el-wire ready-to-wear kits that I've had spotty luck with. Less than four dollars for an LED light string? That's insane, and cheap enough to pack a few spares without adding too much to the "suddenly costing you more than you planned" budget.