Location and part of the country figure into my max. In the east, $50 a night for a decent place with FHU isn't uncommon. Let's face it, the demographics are against you - tons of people, few wide open spaces to make a park, high real estate taxes and utility bills. The only bargains are state and federal lands which rarely have FHU.
As we've progressed west on the current trip, things started to ease up. The highest I've paid on this trip has been $47 at a KOA and we're averaging around $20 a night.
On our retirement trip we stopped heeding south in Florida when we hit the $100 a night line (around Naples). Apparently, all of the reasonably priced places had been sucked up by snowbirds the year before. At $100 a night, someone better comes change the sheets in the morning.