Hi Dan,
£18000 per year after 3 years is achievable - but you will need to put in some hard work!
I'd say that you can buy the equipment you need to get started for around £3000 + van. But you should also allow plenty extra to live on - at least 3 months wages, and preferably more.
It may take a while before you make enough money to live on. So be prepared to take on a part-time job if you need to while you build up your client list.
Totally agree with Ian about the leaflets - I think they are by far the best way to get new enquiries when you start off.
Read the other advice about leaflets on this forum, and get some good books on direct marketing/copywriting too - I learned more from 'Tested Advertising Methods' by John Caples than any other book I've read.
The other thing with leaflets is HOW you deliver them.
Having your leaflets delivered with the free paper is a complete waste of money (in my area anyway). And I didn't do much better with the local leaflet distribution firms.
When you start out, deliver as many as you can yourself, then you can see what response you SHOULD be getting.
If you hire people to deliver for you, there are lots of retired people who enjoy doing it for a few hours a week, and they tend to be more reliable (if a bit slower sometimes).
Once you've got a leaflet that works, consider trying the Royal Mails Door to Door service. The booking process is a bit long winded and they are quite inflexible, but it's the most reliable service I found.
Never book a leafelt drop during, or the week before a bank holiday week - the response goes down the toilet.
One common mistake with new start-ups is wasting money on the wrong type of advertising - ask for advice on the forums before you commit to spending money on anything.
A mistake I made was paying for a large Yellow Pages ad that didn't really work very well. That's not to say big Yellow Pages ads don't work, only that you won't know if your particular ad works until you are already paying for it.
Hope that's helpful, and the best of luck with it!
Matt
www.cleansmartsupplies.co.uk