Actually you pay more for ESPN than for HBO, it’s just indirectly. ESPN charges your cable company at least $25 per subscriber in the appropriate tier (which is usually the lowest tier) which of course gets passed on to you, I can get HBO for $15. ESPN is owned by The Mouse, The Mouse always wins.
Source? That's almost an order of magnitude off. This source says just over $5 per sub for ESPN and ESPN2, which are far and away the highest per sub in the non-Premium tier. Most of the other channels are less than $1 per sub, some much less.