You want to monitor several hundred hosts for only $1 a month? If that is for all of them I may be able to help you. But if that is $1 for all the sites I think you are expecting to pay too little... it would take quite a bit of my time just to set up the monitoring and not worth my time.
If you really don't want to pay anything, you might want to consider settnig up a cheap computer with Linus and installing Nagios. The only cost would be the computer, and it can be a slow, old one. The software is free and will monitor all your sites.
At that volume you would really be better off just getting a small VPS, something with 512MB of RAM or even 256MB and installing one of many open-source monitoring tools Nagios (as nielsencl recommended), Zenoss, Cacti, ect. You would be looking at maybe 20-30 bucks per month for a reputable provider.