Sassy with the evenings is there a friend from school who might help out even just one evening a week? That's what we do at DD1's school - some of the kids whose parents can't get out of work but have no family to depend on get help from other parents. So long as you reciprocate occasionally most people are happy to help I've found. It would help save some money.
Otherwise findababysitter is a great service, or you could put an ad on one of the university websites and you might find a student who is local and has availability.