You can get a decent E string for only a few quid, so don't panic

I use www.stringmail.co.uk, I think there are other good mail order string places out there too.
I use a Hill special E string, which is an above average string, and that only costs less than £3, the most expensive one I managed to find was £6-something, so it's not going to break the bank - you managed to break the cheapest string

well done.
If you're unsure how to replace it when you get it, see if you can find someone to show you how, it isn't hard once you know how but could seem very tricky if you've not done it before. All else failing, I'm sure someone on here could give you a step-by-step guide!