Government Code §41.106

(a) A prosecuting attorney shall fix the salaries of his assistant prosecuting attorneys, investigators, secretaries, and other office personnel, subject to the approval of the commissioners court of the county or counties composing the district. (b) In addition to their salaries, assistant prosecuting attorneys and investigators may be allowed actual and necessary travel expenses incurred in the discharge of their duties, not to exceed the amount fixed by the prosecuting attorney and approved by the commissioners court of the county or counties composing the district. The county may pay claims for travel expenses from the general fund, the officers' salary fund, or any other available funds of the county.