Are you renting just the adapter or adapter + lenses?
Locally, the Letus and Brevis rent for about $100 a day with Nikon / Canon glass.
I've rented a Brevis from a buddy before for $75 sans glass. Wanted to be uber fair and I was in a pinch.
Homebrewed adapters? Dunno - you may want to check HV20.com and see if people are renting theirs out and for how much. I wouldn't be charging more than $40 - $50 a day though at tops with a DIY'er personally.
I don't think pricing should be discussed here. It's specific to each person's local market and open discussions about it could have negative effects for everyone. If you want to know about how a specific person conducts business, PM them.
No need for secrets. If you want to be in the rental business, I believe transparency is a good policy. Go to my website: www.timnaylor.com and then to the rental page. You'll see what I rent my adaptor for alone, with lenses, with camera, etc. I price according to my market and the cost of the gear. I'll be lowering them in the next day or so as the market is getting full and it's paid itself off. I offer two and half day weeks and one day weekends. Have a clear reservation/cancellation, insurance and deposit policy your renter can read in advance and in writing. Taking credit card is a good idea. Sure you pay a fee but it makes business easy which makes more business.
Have a back up plan. Adaptors will go down. I've had three motor failures on various rentals. If not for the good will of other users from this site and FEDEX I'd have been screwed. A back up adaptor is a good idea. If you can't afford it, work out an agreement with a few others in the same boat as you - in short a back up network. And be on good terms with the manufacturer. A time will come when you need parts overnighted. Know how to take apart, repair, clean and re-build your adaptor. Upon check in, immediately check that all is in good working order and nothing is missing. If you wait it may be too late to capture funds from their deposit.
Require the renters to drop off camera beforehand to have it fitted. Sending out an adaptor on its own and expecting the renter to figure it out is asking for trouble. I always fit their camera to the rods/rails myself and insist their AC come in early to be teched on the ins/outs. I value my weekends. Don't believe anyone who says they know your system.
Another idea is renting for 5% of cost (that means, adaptor, rods, baseplate, case, etc). If it's a seldomly used item maybe more. If it's flying off the shelf - go less. Remember these things begin to depreciate as the market gets saturated. HVX's initially in NYC were renting at 8 percent. Now they've come down to earth, to 2-3 percent or less. Also, cut your frequent flyers a discount - keeps them coming back.
For me, I get nervous about renting out my gear. I only did it once, rented my indie dolly to a fellow dvxuser, but I came with it and was the one to set it up and break it down. I keep thinking that if someone rents my adapter and lens for $100 and messes it up, I will not be able to film and the cost of repair may be much more than the $100... But maybe I feel that way because I use my gear weekly and I am in the middle of production on my full feature... So a damage piece of equipment would be a disaster for me (unable to film - reschedule immediate shoots, actors, crew, location etc...)
Maybe if I wasn't using the gear much at all, it would make more sense... :huh:
You'll be amazed how careful people are once you have a deposit for their deductible or the full replacement value. I've made only one claim in two years of renting from a director who damaged an LCD on my BTH 1700. The only bummer is that insurance won't cover you for having to subrent while you wait for repair. Overall, renting out has been worth it.
Most of my jobs are not with my gear, but I still love to have it. So it has to earn its keep.
I agree with Tim, Insurance + deducable will keep your gear cared for. I have only had one lens damaged and the cost was recouped from their deposit. Our rental fee is very fair and requirements are posted on the site as well www.letusextremerental.com
Most of our renters have been familar with the gear, and I am always willing to get them setup.
I rent out a Letus + Canon prime lens set + follow focus + matt box + filters + zacuto hardware + monitor sans camera for around $300-$350/day. I should probably raise it. ;-)