DH and I are in a similar boat. We have hired a baby sitter once when DD was about 12 months old and DS was about 4.5. The babysitter was one of the carers in the creche of the gym I go to so DD was very familiar with her. It went swimmingly. I've also considered using carers from the kids' childcare centre for baby sitting. We've just never justified the expense!!
In the interim DH and I often do/did date nights at home after the kids have gone to bed (with the expectation that it may be interrupted by parental duties). Date night is usually just a plate of nibbles and/or chocolate and watching some stand up comedy that we've either downloaded or watching on You Tube. Cheap and cheerful!! I figure that having a laugh together helps to keep you connected.