Just throwing this out there in case you might consider. Are you able to boondock/dry camp? Our RV is set up totally for off grid including residential fridge now, but even before it was we still did a lot of dry camping, just watched our energy consumption moreso and supplemented with other sources.
We are planning on being in Flagstaff/Sedona/Cottonwood area around Mid May. Have sourced tons of dispersed camping areas. 38ft MH with no toad as we've always travelled for many, many years. If this appeals to you as an option, as it does to us moreso than organized CGs check out Freecampsites.com for one resource, as well others suggest: Allstays, Campendium, BLM & NFS websites.
Have noticed on many posts/forums, private blogs etc lately that folks were really really disappointed with Sedona now being overly tourist and commercialised and wouldn't go back. David Bott = outsideourbubble recent visit; Camperchronicles this or last month write up; JimandBarbsadventures and many many others commented like 2Gypsies did above on their blogs about touristy, nowhere to park, being charged $5 to stop and have picnic at a table etc. These things can if you let them take away from the wonderfulness of the surrounding areas if we let them sadly :(
One Tip for the Balloon Fest - the line ups are hours long, so maybe consider coming in a couple nights prior instead afternoon/night before, so you can set up relax, rejuvenate etc and watch the show as the later arrivals come in. Just sharing and to each as always their own.