Lead works well and is fairly inexpensive. You need to catch them in the act though
Here's a really long story about lead-based rodent control. A friend and I were walking around the block in my neighborhood when we went past a neighbor's house the next street over. He was in his back yard having margaritas and invited us in. We were sitting there chatting when a guy came out of the house wearing boots and a cowboy hat and smoking a cigar.
He sat down with us and just started talking, not introducing himself or asking who we were. Well, he was telling some really outlandish stories and dropping names like Willie Nelson, Jerry Jeff Walker etc. So I asked him if he was a musician. He said he used to be and had had his own band a few years back and had played with Willie and the boys for years but that he didn't do it anymore except for fun. He said he was now a writer. I asked if he had gotten published yet and he laughed and said he'd had several books on the NYT Bestsellers list. Honestly, my girlfriend and I thought this guy was a really charming and funny BS artist.
So I turned back to my neighbor and asked him if he had gotten mice in the winter when they cut back the brush at the city park near our homes. He said yeah. I asked him what he did about them because I was freaked out and didn't want to use poison. He said "I shoot em". I blinked and said "Shoot 'em with what"? He said a 357 Magnum. I started laughing, thinking he was teasing me. Then the cowboy friend said come and see.
We went in the kitchen and sure enough, there were 3 really huge holes in otherwise perfectly restored kitchen cabinets! (We live in an historic neighborhood.) I couldn't speak for a minute and then I said "Well, you can't just shoot them in your house". That's when the cowboy said "Yeah, I told him it didn't work in my house and to just get a cat but he wouldn't listen."
By this point, I'm thinking these guys are a little nuts and maybe it's time to leave. So as we're leaving, the cowboy says we should have another margarita. I demurred and said it was a pleasure and then said I hadn't caught his name. He apologized and tipped his hat and said his name was Kinky Friedman. I thought this was another joke and laughed and said "I'll bet you are". So he pulls up his pants leg to show a pair of custom made boots with the name Kinky across them. Well, then I really thought he was an odd duck so we got out of there fast.
The next week, I came across a full page spread with his picture touting his latest book! The article was long and sure enough, confirmed all of his outrageous stories, but there was no mention of his lead-based rodent control method.