J-Heller,
To add instrument instructor privileges to an unrestricted FI rating will cost around £1300.
ME instructor rating will cost around £2200, but you need 30 hours P.1 on ME aircraft before you can start.
Aerobatics instructor rating probably around £800.
If you have an unrestricted FI and 500 hours instructional time or so you can in principle teach on the CPL course. Stay with a school for long enough and they might (part) sponsor your instrument and ME instructor ratings.
Ps: all amounts are guestimates.
Cheers