As usual, BSOE's got a great solution for you. Unfortunately the "US Coast Guard Approved" label on most of those models is in a location that gets a lot of wear so it may get rejected at the boat ramp if the rangers are checking closely.
Your fallback plan could be to call up rafting outfitters and ask them if they are selling off any used PFDs. A couple where I've had success are Timberline Tours and Lakota Guides over near Minturn. Check the phone book for a toll-free number for them.
Often you can get Type V PFDs that are still in good shape for about $20 or so (they may have wetsuits, booties, and splash jackets too). Just make sure to CAREFULLY inspect the PFD for tears or obscured print on the label that could get a PFD rejected by the rangers at the ramp.
Have a good trip,