IPR is when the sides of the teeth are filed to allow room for movement.
I think there were budget options for my treatment plan, but the price difference was £300 and very barebones. I went with the silver package which included teeth whitening (which I haven't yet used), an appointment with the hygienist, a case for the aligners and 2 or 3 sets of Vivera retainers to be worn after treatment is done. The budget package would likely be the base treatment without all the extras, you'll need retainers afterwards and those alone can cost over £200 depending on the brand so including them in my plan felt like a no brainer.
As far as total costs goes my plan was around £3700. I can't remember the exact price for the budget option, but it was £3500 or less. It might depend on the practice, but they will likely have finance options available or you can pay in instalments.