why does it cost so much just for an hour of training?
You've not specified how much you consider "so much", however it's unlikely to matter too much to the answer. What you're paying for is (at least) twofold, and probably consists of


The rental of somebody else's aircraft. Every hour you fly this aircraft takes it an hour closer to an expensive maintenance window. There are costs involved in running an aircraft much like there are costs associated with owning/maintaining any vehicle. Also, fuel isn't free - its is often rolled in to the cost of rental for aircraft.
The time of an instructor, who himself has spent time/money learning his craft, and quite possibly does this as his job (as in, its his sole purpose to earn money from teaching you to fly). He has skill and experience, and like all jobs, the more his skill/experience the greater fees he can charge.


You may have missed the first rule of purchasing a service - shop around. Is your flight school/instructor of a comparable price to others in the locality? Is the instructor you're using a senior CFI, or a new CPL hour-building to get a job with an airline? You will potentially get a different level of service depending on price, but this may suit your wallet better while still giving you the skills you need to get your own pilots license.

Anectote: When I was training for my PPL (circa 2001-2002) in the UK I paid roughly £150/hr. This included the hire of a C152 and a pretty experienced instructor. From memory the instructor was £80/hr and the remainder was the aircraft. When I got sick of being cramped in a C152 with another 6'2" guy, I paid more to fly a C172 - probably added about £40/hr to the cost.