DSF

I have a customer, wants 5 prints on a shirt x 8 shirts, I usually charge £5.00 per print so it's not realistic to charge almost £30.00 per shirt (including shirts which are sportswear)

I was thinking of £15.00 per shirt for printing + the cost of the shirt?

Thoughts on price, lower or higher?

Lower..... but then you know your market in your area.

Depends on your customers options really and if you've lots of artwork to do too but bespoke work, quality output and service I'd go with what you feel and try it at your price

Sublimation, transfer or vinyl?
If sublimation or transfer then I would gang all five images onto one piece of paper - either A3 or A4 - and charge my going price for that size transfer plus £1 for each extra pressing.
On five print locations that would add up to transfer price + 4 x extras @ £1.
At my prices, for 8 A3 transfers, that would be £8 + £4 extras = £12 per shirt + garment.
If it doesn't all fit onto one sheet then bump up the price accordingly.

If using vinyl then I would charge on a similar area basis but add £1.50 or £2 for extra applications to allow for weeding.

You have to remember that each time you close the press is another time you have had to reposition the garment and another chance to make a mistake.

these will all be vinyl really, i have quoted £15 per shirt, I usually charge £5.00 a vinyl print whether it would be front or back, I've charges £15.00 due to time weeding etc