You don't have to spend £300 to stay rear facing, don't worry! It makes sense to spend a bit more for a seat which will be used every day but I wouldn't go for bells and whistles unless you want to.
This is a very good article which explains all the cheaper rear-facing seats, features, space taken up in the car and how they are used etc.
erfmission.com/extended-rear-facing-car-seats-that-wont-break-the-bank-seatbelt-install/
The Joie Steadi is on offer at the moment at Argos for £70 which would be a really good deal, although I'd highly recommend asking them if they would let you try the seat in your car in the car park. If it doesn't fit securely, the Joie Stages would be better, that's about £120, but does sometimes go down to £99, if you're not in a rush.
Personally I would not bother with the Every Stage because you can get a basic but good booster seat for £30 when the time comes, so the extra £60/£100+ isn't really justified. (The booster mode in Stages is not really worth writing home about - but you do get a little bit more height from it for rear facing.)
If you wanted something to last a bit longer the Britax Max Way is about £180 now which is the same price as the Two Way Elite. These last until 6-7 years on average, whereas the Joie seats can rear face up to 3-4 years depending on the size of the child.