Right for the plants and drift wood try Jave, they are really cheap and will have your order out to you within a week. They advertise in most fish keeping mags.
Here is a pic of my tank with Java plants.
The best way to save money is make sure you do a full tank cycle before adding fish. Make sure your parameters (Ammonia, NitrIte, NitrAte etc) are ok before adding fish. If you add fish too soon then you will end up loosing them to stress etc.
If you are going to use gravel then it may be advisable to buy a large bag (this is normally cheaper than buying those little tubs that pets at home sell for £3+ a tub. I got a large bag of gravel from my lfs which cost me £8.99 and would probably equal about 10 of those piddaly tubs.
Make sure you clean the gravel fully as you really don't want manky water.
Buy a decent filter (this is where the cost will go, unless filter is included with your tank, don't forget hood and light too.)
£256 sounds like alot of money, especially a youngster like you and well done for saving so much. The problem with this hobby is it is very addictive and can cost in little things like water treatments (which are handy to have standing by just in case) and it is a really good idea to have a water test kit. You should be able to get one of these from pets at home for about £17, this is really a necessatiy in the long term, short term your lfs will test your water parameters.
Sorry for the long post.
Kaz
p.s. Before buying any fish, look around ALL your lfs's, look at the fish they have, do they all look healthy which seems to have the healthiest looking fish, this could be the one to get your fish from. This is where your money will go actually on the fish themselves if you buy from a poor place (it may not be advisable to buy your fish from large places like pets at home etc as they don't devote their time to the fish etc as they have other duties, look for smaller places which seem to specialise in fish.)