If you're taking never-evers, hopefully they'll be riding on rafts rather then paddling into the maw of Skull and Sock-it-to-me! A good place to get cheap, quality PFDs is to call the rafting outfitters along the route and see if they've got any old PFDs that they're selling off. Usually you can buy a used Type V PFD for about $15 to $25, depending on the condition, which is quite a deal considering that they're about $100 new. I know that Greg at Timberline Tours may have some to sell. He can be reached at 970-390-3020. I've also picked up good, used gear from Lakota. Sometimes outfitters will have other gear like wetsuits, booties, splash jackets and so forth.
If you want Type III PFDs for kayaking (or just more comfort), try the BOC or other places that have kayaking lessons sometimes they sell off used gear.
If you don't want to buy the gear, some outfitters will rent to you for the weekend, if they don't expect to be too busy that they need it for their own clients. There's also a place in Fruita in the train car by the dinosaur museum (south side of I-70) where you can probably rent the PFDs and other gear.
Before you buy, just remember to check out the PFD labels and make sure they're still legible and check the PFDs to make sure they are in good condition (no tears or holes). Let me know if you need raft support. Have a good trip!
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse