You have quite some demands for your budget I think it will be very hard to impossible.
100% uptime on server-level is also not something anyone can guarantee, as hardware can fail.
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You can try the Dedicated servers offer forum. On that forum do a search using the keyword "$100" and look for offers suitable for you.
Although I believe you will are going to have a hard time in finding servers with the specs you want with this budget.
For starters, 100% uptime doesn't exist. If someone does offer it they are just using it as a marketing gimmick. It's impossible if you don't have redundant hardware, power, and network; all of which you will not find for under $400 nevermind $100.
Aside from that, contrary to what everyone else is saying, you should have no problem getting that server configuration for under $100. Try contacting a few providers on here and I'm sure they'll be more than willing to match your price.
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I Like sagoNet, for $79.00 you can get exactly this you want (so you can spend more on additional disk space or raid...)
If you are in the spirit, VolumeDrive (who went some heavy catastrophes in august-september) can be an option. The ~100% uptime may be an issue.
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I found also good quad cores on server4you:
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There are some more budget servers in the US.
I've been a customer of sago net, the first option I said, for years. They had some problems the beginning of this year and recently I noticed some unstabilities that I can't say for sure its my backbone or theirs (from some places occasionally I can't access the server while from others I always can). But generally they are good, and I noticed its network speed (currently, as of 2013-10-06) is better than VolumeDrive. Could have been routing to the place I tried the download anyway.