Check for a local TV repair shop, they usually do it quite cheaply, or a Computer repair shop, after all it is only a circuit board.
It might even be cheaper to find one outside your area, as no doubt the shop rents/rates are expensive, which might explain the £50 charge, which might be a minimum charge.
If you decide to try it yourself the easy method is to cut the faulty capacitors legs, near to the capacitor, then solder the new one onto those legs. This not only makes it easier but prevents damage to the board.
It might even be cheaper to find one outside your area, as no doubt the shop rents/rates are expensive, which might explain the £50 charge, which might be a minimum charge.
If you decide to try it yourself the easy method is to cut the faulty capacitors legs, near to the capacitor, then solder the new one onto those legs. This not only makes it easier but prevents damage to the board.