Just to add, in addition to the costs already mentioned that you would incur from a pets at home bunny rather than a rescue one, you also need an entirely seperate setup for the other bunny to live in until they're neutered as un-neutered pairs must not be put together especially if it's a male/female pair. Even if your current one is neutered (apologies if I missed that bit, just skim-read), if you introduce an un-neutered bunny they're very likely to fight and even though you can then seperate them until they're neutered, lots of people find that pairs that fought before being neutered won't accept each other after.
The £30-60 adoption fee may look steep compared to a £20 pets at home bunny but they come fully vaccinated (£25-35) and neutered (£60-100).
Approximately how much money can you spare for a setup? There are cheap ways to do things. They may not last quite as long, so it is better to shell out more initially, but they should last a good 3-4 years and by that time you may be able to afford a better setup.
Is anyone in your family good at DIY?
http://www.ebay.co.uk/itm/Sykes-mas...et_Supplies_Small_Animals&hash=item51aad34cb3 here is a good basic setup (6 x 2 x 2 run with attached 6 x 4 run) which is nice and secure with very small mesh and nice solid construction. Whilst it's not quite the RWAF recommendation of 6 x 2 x 2 + 8 x 4 run (it is 8 x 4 minimum, not 8 x 6), it's a very good starting point and it's all in one so it's great. Your current one is nowhere near predator proof - a cat/fox/dog could easily get in and kill bunny. The 3 foot hutch doesn't allow enough shelter - a bunny needs to be able to take 3 hops in a sheltered area or it's not really fair on them. You could use that setup and either extend it using aviary panels (available off eBay) now or later on. Or you could just buy an extra run and attach that. A good way to attach the two is to get a cheap cat flap, cut a hole in each piece of mesh and then attach them together with the cat flap. Maybe take the flap out if you want since it's not necessary, it's just a good way to make a hole.
If you line the bottom of the hutch with lino (places will often give you offcuts for free) and put some silicone sealant around the edge, it'll protect the bottom of the hutch and make it last longer. A simple tarp over the top of the run will mean bunny can be in it 24/7 regardless of the weather. It think especially in England it's important to give some rain protection. The clear tarps are better as they're 100% waterproof, but more expensive. A cheap one will do for now, or even shower curtains can work fabulously.
Definitely stay away from chicken coops like this
http://www.ebay.co.uk/itm/1-6m-5-3-...2?pt=UK_Pet_Supplies_Dogs&hash=item1c2a023f98. They are NEVER big enough, and the inside compartment is often absolutely miniscule. They are hard to clean and almost always terrible quality.
You mentioned a shed. They're fabulous! Wooden sheds/playhouses can be an absolutely great piece of accommodation. I don't know if you have one there already or you wanted to buy one, but they usually work out more expensive than a hutch/run combo - however, they can be used for other things at a later date and they give a great size indoor space with lots of height. Then you could just add a run on
http://www.ebay.co.uk/itm/MASSIVE-R...et_Supplies_Small_Animals&hash=item35c6f9d88e and as long as it's attached 24/7 you can get a 4 x 4 playhouse/shed instead of 6 x 4 if you wanted to save room. If the bunny is never shut in, it doesn't matter if it's not 6 foot long as they have the outdoor run to stretch and hop in.
I would advise against using 'custom-hutches-and-runs' on eBay, but there are plenty of other sellers who sell good runs:
http://www.ebay.co.uk/itm/PANELS-TO...et_Supplies_Small_Animals&hash=item257cd2a3dc.
It can seem very daunting to begin with, but many of us have been in your situation where we think we've done okay for our bunnies but we've been completely mis-informed by pet shops. I know everything probably looks very expensive but it's definitely worth it. Perhaps your parents would help out if they know that what you have is inadequate and unsafe? Although I know many parents don't want to know. Here is a good link
http://www.rabbitwelfare.co.uk/ahutchisnotenough.htm and it has some great advice leaflets on the right hand side that you could print off or show them if you wanted.
Everyone on here would love to help you sort your setup out!