A FI(R) will earn £12 -£15K a year full time if they are lucky. My advice would be to only instruct full time when all your over ratings are in place and payed for as you will barely be able to live on an instructors salary let alone save for further training. Alternatively instruct part time. I presently instruct 1 day a week and manage to get 25% of the hours my full time colleagues get working 5 days a week.
cheers
MJR