Crazy one-way fee fluctuation
 

After keeping tabs on Kayak for a one-way SEA to BOI off and on for a few weeks, with no signs of flux from a pretty horrific (to me) $800 for 3 day rental, booked rez with Hertz (carrying lowest fare- don't rent enough to have loyalty). Then realized I should have made it for compact, not economy. Cancelled rez, back to Kayak and suddenly there's a Thrifty one-way for about half what i'd been seeing.

I grabbed it of course. This morning Kayak is showing prices back up where they were. The flux was mainly in the drop fee (from $500 to $223) but the others were slightly lower too, I assume calculated as a percentage ala taxes.

Was this a freak thing or is that kind of flux common?

Have a look around the Dollar/Thrifty forums to see an important difference in their business model for one-ways:

Hertz, Avis/Budget, and National/Alamo cater to daily rentals. So for one-ways, their daily rates are higher than roundtrip, with no separate taxable "drop fee." Ex, roundtrip $45/day, one day one-way $85/day, 2 days one-way $80/day, etc. As the number of days increases, the predicted daily mileage decreases, so the daily rate adjusts accordingly. This works best for long distance, short time rentals, and daily business travelers.

Dollar/Thrifty has a flat rate, separate drop charge regardless of days rented, added to the same low daily price as roundtrip. Ex, one day at $30/day, $500 drop charge, or 7 days at $30/day, same $500 drop charge. As the number of days increases, but the drop charge remains the same, pricing approaches and can even be lower than the other brands. This works best for short distance, long time rentals, and some leisure vacationers. The result is fewer transactions, which allows Dollar/Thrifty to have a smaller fleet, with fewer employees, but more revenue per transaction.

If you're doing 3 days, the first example is probably a better choice for you.