I'm not up to speed on rotary wages but I can say with a degree of certainty that you will not clear £2000 a month in fixed wing instructing. Indeed you would be lucky to earn £1000 pre-tax in full time fixed wing instructing initially.
Although these wages don't necessarily carry over to the rotary world I can't imagine the gap would be huge.
There are many first officer airline pilots who struggle to take home £2000 a month...
Good luck though!