75W GU10 halogens are around £2.80 +VAT at my wholesaler - even on Amazon they are under £4, like this example;
http://www.amazon.co.uk/Bell-63mm-GU10-240V-Degrees/dp/B000VI1SCK
Not sure where you looked to find them at £11 each...?
When looking at LEDs the important criteria are light output (Lumens) and colour temperature (in degrees Kelvin, K). It's odd that bulbs have always been traditionally measured by the power they consume (in Watts) rather than their light output.
For what it's worth, your 75W GU10 halogens would be around 1100 Lumens, yes, but the colour temp is quite cold at just 2700K.