Mike..
Everything from a few fringe benefits to +50%, the regulator being supply and demand.
In some airlines the sim breaks from exhausting E-W flights is enough to supply instructors at no extra cost, while the unknown 3rd world startup operator must have enough expat TREs to get the show going, and that is reflected in the extra pay.
If you compare a busy TRE with a line pilot in such an airline, the extra pay may be up to 10-15.000 USD/mth, but only as long as the demand is there.
Just like with line pilots - no premiums are paid for high standard or quals - only for the minimum required to fill a slot. In the current environment that means: if the TRI/TRE/CP walks - the pay goes up; if they stay, the pay goes down. Simpel, isnīt it.....
T.