We use the pari's with everything. They last for 6 months, can be boiled. The RT at the clinic gives us a bag of them when we ask. Otherwise I've purchased from American Allergy and I think ihealthdepot.com where I purchased the pari proneb ultra II for DS had some at a good price, too -- though I don't know what they charge for shipping -- that could be cost prohibitive.
I've never dealt with insurance covering them 'cuz it's been too much of a hassle -- doctor has to write a script, get the home health store to carry that brand... If you're on Tobi, have you checked into the tobi foundation program. If your copay is higher than $25 and you meet income requirements -- they'll pay what insurance doesn't cover. You have to get your tobi from CF Pharmacy, but every other month they'll send you a pari neb cup, too. If you're on pulmozyme, gentech (sp) also has a foundation to help defray drug costs.