I've going to have some deeper dives (110-130ft) this coming season. I'm wondering if nitrox is worth the cost for the wee bit of extra bottom time! I ran the numbers on my Perdix (medium conservatism). At 130ft with 28%, you only get 3 more minutes of NDL time than on air.
At my shop, I'd pay $14/tank (up to 100cft tank) for custom mix (you can get banked 32% for $12/tank). In addition, I'd have to have a pair of tanks O2 cleaned ($50/tank, so $100).
Most of my diving is only 2 dives a day. Occasionally I'll do 2 Lake Michigan charters in 1 day (4 dives), but most of those are shallower (less than 90ft, most under 70ft). I have a trip to the Straits of Mackinac in June (3 days of 2 dives each) and Toby in July (1 day of 4 dives 1 day of 2 dives). I'll be taking my own tanks on the Straits trip, and am up in the air about the Toby trip (Divers Den only has 6 HP100 tanks for rent) - I refuse to dive aluminums now. Screws with my weighting.
I got a pair of tanks O2 cleaned last summer, but I really only used the O2 cleaning when I was on my Alpena, MI trip. I could have easily done those dives on air.
I've debated this with several friends and they all just do deeper rec dives on air. I didn't get my new doubles setup (tanks I already had) O2 cleaned, either.