Hi jayjay, i started about 7 years ago with around that amount of money and its been the best investment i've ever made
to start with go to a company called soap national they are one of the cheapest suppliers of window cleaning equipment on the net.
Don't bother going for the dearest squeegees etc go for a name called pulex there cheaper but do the job just as good as any
I personally use a bucket on a belt when using ladder work as it's a lot safer but not everyone does so its down to personal preferences
I use gg4 as a soap in the water its very concentrated so it lasts but if your budget runs out on the essentials then just use fairy i don't like it but i know a lot of window cleaners use so again it what you prefer.
There are plenty of good ladder suppliers were you should be able to get a decent double for under £100 or do wot i did and get a decent secondhand one, my first ladder cost just £15 in the local paper and that lasted me a year by then i had a decent round going to buy a new one
I don't think you can beat knocking on doors for customers seem to get a better response that way but others seem to get a good response from leaflets so maybe you should try both to start.
hope this help its a start, whatever happens don't give up i nearly did and know i have well over £4000 of commercial/ private work , i also recently converted to wfp had its the second best move i've made
GOOD LUCK!
REGARDS JOHN.