Greg,
Simply math, the U.S.C.G. requies that the lights have to be S.O.L.A.S. certifield which drives up the cost:
http://www.sailgb.com/c/lifejacket_lights_spares_rescue_lights/
Whistles (sound making devices) also add to the cost.
Although you can shop around (West Marine, etc.), it'll still cost you some serious amounts of cash to properly equip a passenger carrying vessel according to S.O.L.A.S. standards.
All of the Regs regarding lifejackets can be found at this site:
http://64.233.161.104/search?q=cache:3mU...&hl=en&ie=UTF-8
All lifejackets must 'accessible' and be in 'serviceable conditions,' at all times, as well. (Loose threads, loss of reflectivity, oil stains, etc. and they're no good.)
You loop the lanyard of the lights and/or whistles through the two small loops that many of the better Class I jackets have.
It's a given that you're going to spend at least $350- $400.00 for a six pack charterboat's required lifejackets without 'going too far overboard' (very bad pun).