A work colleague of mine's father is an instructor and he charges €30 if the learner goes in their own car, €35 in his car, a minimum of an hour instruction - could be up to 90 minutes if he has no other lessons immediately after -
price includes book/dvd loans, rules of the road and under the bonnet instruction which he apparently does for around 10 minutes a lesson.
Shop around, before you book ask them exactly how long each lesson will last and what will they cover, in the long run it's worth paying for proper lessons if it teaches you all how to drive safely/correctly rather than just getting you through your test.