eBay and Craigslist finds

That is exactly the type of feedback that I'm looking for, thanks dude!

How much would one expect to pay for an 'entry level' road bike? As I said above, all i'm really concerned about is getting a good frame as I want the bike to be something of a project that I add to and improve as and when I get money...

You just need a bike that'll do the job, as for finding a bicycle, it varies, it can range from free to £50, try and look around, car boot sales, ebay, garage, relative, etc.

as long it's in good working condition, changing it into a singlespeed doesn't take much effort.