During the transitional time between Domitian and Severus, pay for military personnel stationed on Hadrian's Wall was as follows:
-Legionary: 300.
-Ala trooper: 200.
-Auxiliary infantry: 100.
Additional pay for soldiers that had a particular skill (i.e. musicians, clerks and medical staff):
-Pay and a half.
-Double pay (duplicarius - a term sometimes seen on legionary's tombstones).
For further information consult Companion to Roman Britain by Peter A Clayton.
Does anybody know which emperors after Severus increased the pay of the legions? No doubt, in order to secure a healthy transition to power, most of the 3rd Century emperors increased, or at least promised to increase, the pay of their soldiery.