The cheaper alternative is to belong to a babysitting circle.
You get to know other mums and children that way too.
We did this when my children were young (but maybe more Mums work now so have less time and more money)
We had a monthly coffee evening, one group I was in gave everyone 12 tokens (curtain rings) worth 1 hour and you sorted out your own sitter, then after I moved I joined one where we took turns to be secratary and find sitters, & keep record of points. (double after 12? or 11?)
The snag was that the people who didn't go out much were the one's who were free to sit, so some people were short of points, others did more than their share.
I suppose you might get round this if you had someone who would sit for cash, and you could use them when stuck, sell points to people who couldn't keep up.