If you're not adult and living with parents it's crucial to have their full support. There's no way you could provide for them if anything goes wrong, vet bills are very high. Parents also have to be very understanding and tolerant (for example: the space they need, companionship, correct housing, adverse weather plan B, natural odours etc etc)
Out of my multi-pet household my guineas cost the most. It really isn't just the initial cost and then food and bedding bills.
Unfortunately, if you don't have supportive/understanding parents it's a bit of a risk. You'll get upset if they get ill and parents refuse to take them to the vets due to bills. So, ensure you've sorted this with them before you get any piggies, as well as appropriate housing. Don't settle for "that will do". After all, you're taking on living creatures that fully rely on you.
I wanted many different pets whilst living with parents and had to wait to move into my own house to be able to have them. Strangely, now I could have Anything, yet iam more careful and understand why parents were reasonable and taught me limits. Guess that's the difference between responsible pet owner and hoarder!
I work full time. Only way you could fund it is if you've asked for money for b'days etc and spend all your pocket money on them. But still be aware your parents will be the one expected to pay for vet bills and they might not want/be able to. Guineas are quite fragile creatures and have complex health problems.