We looked into Math-U-See. It looked really good, but there just wasn’t any used curriculum out there.
We bought some workbooks from Sam’s club for $6 each that taught all the basics that more expensive private school curriculum taught and started with Saxon 54 in third grade and just went at the kid’s own pace.
You sound like me - we always buy used curriculum when we can! We use ebay and some local co-ops where parents can come in and buy, sell or trade used curriculum.