Specialty glass rental can be an affordable alternative to actually owning some of those bank-buster lenses. It isn't cheap, but a couple hundred for a one shot use as opposite to several thousand certainly makes it an attractive option for many people.
A couple of hundred??
I've rented the 100-400mm a couple of times, and the cost was $35.00 each time. I'd pick it up Firday evening (for a Saturday rental). Since the store is closed on Sundays, I'd return it on Monday. Basically, I was getting better than two days worth of rental for one.
I'm also considering renting the 400mm IS, which costs $70.00 per day.
If it was a couple of hundred dollars, I never would've considered it...