Hi @lastmjs!
Each HTTP request costs currently 400M cycles flat fee plus cycles per request and response byte. The max response size is taken as a parameter for charging and the default is 2MB which makes it really costly. You must set the max response size to something in the range you expect in order to not be charged insane amounts of cycles.
Hope that helps.
We are currently revising pricing, so the pricing for this feature may change. Currently it is rather conservatively (expensively) priced.