There was mention of a high school student after school - you could go with an even younger "mother's helper" for even cheaper, if you mainly want help while you're also there. This can be an excellent option for a summer baby when kids are out of school, too - you could hire them nearly full time or just as much as you need, and pay under minimum wage because they're kids and basically just playing with your kid and getting experience for solo babysitting later.
I also wanted to suggest play dates. Get to know other parents, and in particular, stay at home parents, in your area, if at all possible. May be difficult if you aren't part time or SAH now. But if you can work up to where the kids and parents feel comfortable doing drop-off playdates, hello freedom. Even if you don't feel comfortable with 2 toddlers + baby, I assume some parents would be interested in evening playdates or date-night kid-watching trades. We're pretty comfortable with drop-off with our almost 3 year old now, but we often used to do post-bedtime kid-watching swaps.
Are there programs in your area for new parents and/or second time parents? We've made some great friendships through our local "Program for Early Parenthood Support" here in Seattle. I've heard MOPS is great, too. The PEPS investment was only a few $100 but sooo worth it.