Thanks Elena!
Those rates seem the same for everyone I asked, although they do have a special student rate which is slightly cheaper, but only slightly! Also I think they have another rate for people who only sell lower priced items like cards, but not sure how much it is.
You can also pay in "installments" but the only option they gave me was 2 installments over 2 months, and they don't activate your account until it's all paid up so that seems pointless.
I decided against saving the money to join since for me personally it worked out that I'd have to sell 150 ish items before I made my joining fee back, which seems like a huge amount. The percentage they take includes shipping costs, so your profit is lower than you might first imagine.
Another bad point I heard about them is that you can't adjust your prices if you also sell elsewhere. For example, if you're selling something for £20 + £5 shipping on Etsy, you'll pay a fee of 3.5% on the £20, plus the PayPal fee. If you're using NOTHS, you also have to sell it for £20, but you'll be charged 25%-30% +VAT on the full £25 transaction. You're not allowed to put it up for say £25 instead of £20 to help cover fees. I heard from a lot of sellers that they regrettably had to put up their prices on all platforms just so they didn't lose out too much on NOTHS. It may not apply to everyone but it's something to think about.