A prescription is a single item on the form irrespective of the number of tablets. My charge for a prescription didn't go up when the doctor doubled the dose.
You don't need a 8 weeks supply per item - you want fewer prescriptions therefore 6 months supply per prescription. You may find however that a doctor is unwilling to prescribe more than 3 months supply in one go.
It's interesting to see the wholesale prices for the medication you may be taking. Most of my (generic) prescribed medicines comes out at less than 50p packet (£1.50 to £3 for a three month supply) but I once had some "paint" for a foot infection that was £160 for 10ml and I went through 5 bottles.
Prices found around 4 years ago when I first started taking long term prescribed drugs.