Excluding the non-powerlifting and other extraneous elements of my home gym, I spent a whole lot less than your plan. Here's how.
- Craiglist squat rack: 300 dollars. Took two weeks for the posting to appear. (NB: I sold the rack for just under that amount, 2 years later. Not bad.)
- Cement floor. Piece of scrap plywood for deadlifts.
- Barbell and 300 pounds of plates, found on craigslist, circa $150
I don't use a bench because I don't bench, but used benches are cheap cheap cheap and making it yourself doesn't sound that hard either.
How can you make your plan cheaper? Well, decide for yourself. Buying new is expensive. Buying 400kg worth of weight is expensive. Buying gear you don't need is expensive.