6 months at £300ish /day = £30k which I haven't got.
Additional project costs would eat up another £10k.
The biggest problem you'll face is even if you created this 'service' how are you actually going to then make money - which requires advertising (either bricks+morter type or viral). And this will cost far more.
Are you 99% sure that what you've in mind doesn't atcually exist already?
And having run web development departments and been in the industry since before the dot.com, I've seen vast amounts of cash/time spent for little/no return. Mostly by folk who didn't actually understand the basic industry they were operating, but could persuade Directors that these were must haves' - so they usually did alright.
The only time I've seen 'little' guys make good money was by creating something that either a FTSE/Global wanted, or that they saw that it could impact their market. And then they are bought.