Yeah, our vet charges 40 ish quid for spaying too. It was cheaper than the injections!
If you contact your local Cat's Protection League they may be able to hand out a voucher towards the cost of neutering. They were ace in my case as they give them to anyone who inquired - you didn't even need to be on benefits or anything. very straightforward! But I guess other branches may limit the vouchers to low income people who can provide proof. So in the end I only had to pay 12 quid! yay!
Edit: Some vets allow you to get the kitten neutered at 6 months, others go by weight : 2kg. Most vets will also agree to spay if the cat is showing 'signs' earlier than 6 months too but 6 months is about the benchmark whatever happens.
I personally would not put the cat out until approx 10 mths - 1 year old and certainly not before injections or neutering. Others have different attitudes towards this though and it very much depends on the cat.
My kitten is 8 mths and totally scatty and I feel she can't be trusted out on her own yet so she will remain a house cat until she has calmed down a bit (in terms of mental kitten - ness) . She gets into enough scrapes at home so I dread to think what would happen if I let her out!