OK, look, this is genuinely entirely up to you but let me say one thing. Marketing makes money. So this isn't about how much it costs. It's about an initial investment to make more money later and just managing that sensibly.
There's a solution here for everyone, so check these choices and .. get in touch so we can work something out for you.
If you want me to develop your business online then everyone will be different so I can't give you a price right here and now, but I will say that talking about it is free, so why not pick up the phone, let's talk it through, and I'll put together a no-obligation proposal. We will discuss your means and I'll put together something you can afford. I'm working with a few local businesses now for just £200 a month. Easy, right? Especially when it can double your business.
Of course a fully fledged Internet marketing programme with some muscle behind it can cost tens of thousands of pounds spread over an extended period.
If you already have an established business, you know Internet marketing, you just need a crack team to handle a particular project, do get in touch .. I'm putting together Surge Marketing for exactly that purpose.
If you want basically to know what to do, but don't want to pay someone to do it (you want to do it yourself), then A Million Tweaks is the thing. From just £20 a month I'll guide you through the Internet marketing maze. If you find a barrier, I'll get you through it.
If you want FREE, take a look at my site Flow Marketing. OK it's not finished (none of my own sites are :-) ), but it is free and the idea is that it will steer you properly towards doing the right thing. There's a lot you could do in Internet marketing, the trick is not to waste your time, but to do the right thing. Flow marketing will guide you and if you hit a dead end, let me know.
All I really want you to know is that I can probably help whatever your budget so don't worry about that.
Why not get in touch and let's see if we can work something out.

Birdgate Dental Practice, Pickering
"Thanks for all your work, 3 new patients found us this week from the website!!!"

Sea view bed and breakfast in Scarborough
Measured on 31 March 2011: Website enquiries 6x better than average, 4.4x increase on own performance last year.
Curing putting yips (business up 6.12x year on year .. feels good (the low-fi website style isn't mine, but is retained deliberately))

(Grew online business by six times in twelve months)

(Online business grew by 2.5 times in 4 months)

Stop house repossession
(PPC ads and SEO .. results coming soon)