I'd say the best thing to do is find a "commercial script" (a script that must be purchased.) Then survey other sites and get a idea for what they have and how you can beat it.
I honestly in a sense don't think it'll take $x,xxx+ for this project assuming you outsource it. oDesk.com is your friend 
In any case, here are some straight tips:
1. Use a commercial script to start up, once you start generating income, then have a custom script written
2. Work with some auto advertisers to offer exclusive deals to your members that they'd love
3. Promote using PPC search marketing and I'd also suggest a few PRINT publication advertisements. Find the right magazines and you'll be successful *(assuming it doesn't cost a arm and a leg for the advertising spot.)
4. If your using a commercial script (which I'd suggest over an open source) - you can also hire programmers to create enhancements for the system. Once again, oDesk is your friend
5. To start off, I'd say offer affiliate programs as well in conjunction with personal advertisement on the site.
When starting off, I'd say the most you need is a shared hosting plan but as someone said above, once traffic starts rolling in you'll need a dedicated server. Although saying you'll need 2 servers is pushing the envelope a bit.
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