Whether you call yours a "compost keeper", a "compost bucket", a "kitchen compost bin", or whatever, I am sure you do not want to overpay for a new one. I have some ideas for you.
First off, the cheapest compost keeper I could find online at the time of this writing was one for under $15 from Biobag. When we consider what goes into a compost keeper, and how we do not want it to smell up the whole house, it is good to note that low-priced model rates high with customer reviewers on Amazon.
Still, you do not have to buy a compost keeper online to save money at it. In fact, you can find them at Goodwill stores. I have seen new ones for sale at Goodwill -- and those good folks always offer new items at a nice price. Of course, on a lucky day, you could find a used, good-condition compost keeper on the housewares shelves at Goodwill. Nothing like a little reduce, reuse, recycle action to keep with the green theme of composting waste.
As for yard sales, tag sales, and the like, I would not expect to usually find a compost keeper in that situation.
More likely, you will find folks selling compost keepers on everybody's favorite online yard sale, eBay. Graciously as ever, I have provided you with some eBay links below of current auctions going on for compost keepers.
I hope I have given you enough options to find the right compost keeper for you at a price that works. Happy composting!