I would certainly love to be able to try out cable without the pressure that a 30-day return policy generates (I always feel like I am really buying it and can only legitamately send it back if there is something actively negative). Your model also has the benefit of encouraging people to try cables they really cannot afford (a good thing in my mind - it helps to know what you are missing).
However, your cost model seems VERY unrealistic unless your membership was large and number of cables small (which has other problems in terms of availability). In pro-audio rental, the base rate for rentals is 1% of MSRP per day. This assumes that units will be in active rental for about 3-5 years and will be rented out for 50 to 75 paying days a year (longer rentals get discounts - e.g. a week rental costs 4 days). At this rate equipment pays for itself during the second year and still has 2 or more years of profitmaking rental. Renting cables would have to be for at least one week at a time with a week being sent back and forth. So with a total of 3 weeks per rental the absolute maximum number of yearly rentals is 17 and realistically even 15 would be difficult (also one week is not very long for evaluating cables). So at 15 rental a year if we want the cable to pay itself off over say 2 years you would need to charge 3.4% without allowing for ANY profit or administrative costs during that period and assuming that the connectors and cables will last through 4 or 5 years of such heavy use - which I doubt). I believe that realistically you would need to charge something close to 10% of MSRP for this rental library to work and since used cables can often be had for 40-50% of MSRP you are asking people to pay 20-25% of what they could buy the cable for, just to rent it for a week or so. And then there is shipping both ways...
Not to be glum, it would be great, but unless some wealthy benefactor of audiophile land is sposoring the venture as a community service (or tax write off), I doubt it could work.
Good luck
