register many domains for few dinero? How

I'm tire-kicking an idea, and it would involve registering a whole slew of domain names, and if the idea works, i could end up needing to register a slew times 2, times 2.
Visualize the Don Alm idea: a home at 110 Main Street is for sale. So you register the domain, 110MainStreet.com ... and market it to the realtor or the home seller.
Now do this for 100 homes ...
Any ideas how to avoid paying $8 to $10 per domain name to register 100, 200, maybe 500 domain names over the next month or two?
I just don't have that kind of money - nor that kind of confidence in this plan - to invest.
Thanks for any input you can provide.
Robert J.