Cheap will not get you there.
I beg to differ, having run some businesses, web based, and offline too. Here's the basics of how we did what everyone says cannot be done:
For starters theres difference between 'cheap' and 'lean and mean', although the 2 are infact the same. This proof is taking into consideration of some inbound linking work, so not completely link-free, as that would be inpossible web-wise - but 100% seo agency free!!
A basic website for £50 was built, was a few pages long and that was it. Next we got a free line listing with YP, then did a ton of link exchanges (please remember this was many moons ago when it could be done), mabe about 300 swaps, then bought a few links to pull in the enquiries - but no seo agents needed.
The YP got us over 200 clients over about a year, then we got about 400 free links, one ways inbounds, and left it at that. Pulled in about 12k, pure profits, but due to competition, we binned the biz, to operate an SEO style website, but not as SEO agency, it was different - more of an ad space flogging site, made some cash and binned that as it no longer interested us.
We have set up about 9 sites over the years, so are experts, and won many awards to boot. So there you go, a brief intro in what can be done if you are willing to be clever and not so keen to open the wallet.
Another site we owned got over a million visitors to it - all free, we never paid a ££ for that traffic - ever. Its like taking Candy from a baby, it really is...