For me, the answer has to be,
"More than expected".
The amount of times I have found myself justifying - "it's only ?0.59..." yada, yada, yada, "...a cup of coffee costs more than that!"
One question I prefer to ask myself is, how much I have actually spent on apps that I have:
--Used once and never used again
--Used once and stopped using it because it was so poor
The trouble becomes when it stops delivering value - and have you re-couped your money's worth with its usage?
Dread to think what this figure will be, 12 months from now. Doh!