Uk Instructor rate
I asked this of an instructor I had a trial lesson with a few weeks back. He said most places pay £40 per hour, but of course for each hour flying you do an extra hour for pre and post-flight briefings. You also don't get paid for teaching groundschool. He reckoned at his school instructors get between 30 and 60 paid hours per month dependent on season, averaging out at around 45 per year. So, that's a shade under £22k.
Apparently some places still also pay a small salary retainer on top of that, but it's rare and those that do are looking to scrap it for new hires. Plus side is the retainer usually stipulates you can't work for anybody else barr that school, where as if you're only paid for the hour you're free to work elsewhere when that school has no work for you. (Though it's frowned upon if the're based at the same airfield.)
Please note I am not (yet) a practicing instructor, this is all second-hand info and maybe incorrect or inapplicable to many companies.
Si