Hi Fishkeeper, welcome to ukaps!
You've made a very good start with your tank, even with your algae issues. I can understand tight finances, and maybe I can help with a few other suggestions.
First of all, listen to ceg. He really does know his stuff!
Secondly, do some reasearch before you spend if you only have a little to go around. If you do consider a rescape, then consider Akadama as a substrate. Its a bonsai 'soil', so its cheap, and available in large bags. Cost me about £20 for my rio180. Have a read up about it here
http://ukaps.org/forum/viewtopic.php?f=17&t=741. It absorbs nutrients, making them available to plant roots, just like the expensive substrates.
More urgent is flow. Its recommended that you have a minimum flow thats x10 the volume of you tank, per hour. Ceg recommended a powerhead. Many here use koralias, as do I, but you could try a cheap ebay version. Theres one offering 3000l/hr for a little under £20. A lot of this stuff comes from Hong Kong, doesnt mean its bad!
I also upgraded my juwel internal filter pump. If yours is the pump 400, then you simply buy a new impellor for the pump 1000, and you'll instantly have a 1000l/hr filter. Think I got mine on ebay for £10-15. If you need more flow at the substrate level, you can attatch a spray bay. A fluval spraybar kit is £8.60 from pets at home, and you can fit it to the juwel pump outlet.
Some form of CO2 is also good, but needs to be consistent. One DIY unit will lack that. 2 or 3 units will help even things out, but could be hard work in the long run. As said above, the forum sponser Aqua Essentials is now selling liquid carbon (branded Aqua Carbon) for £4 for a small bottle, which is a good cheap solution. You would have to remember to dose every day, but its much less work than DIY yeast mixes.
Consider reducing the photo period. 6 to 8 hours per day is usually a good start. I use a cheap plug socket timer - £4 bought from tesco. Maybe have the lights on from when you get home from school, until 11pm? That way you can dose anything just as the lights come on. This may even prolong the life of your light tubes... but thats just a guess.
Anything else you need, try the For sale/Swap/Wanted forum, or try finding it on ebay. I just got myself a new 1200l/hr unbranded external filter, with media, for £36 delivered on ebay last night. Its a risk. It could be a heap of rubbish, but if it works then it'll be a massive bargain!
I hope that helps.
Dsandson