BLS doesn't require much outlay
I bought one of those colonial wodden ones with removable tray from the op-shop - can sit it right into our table. Or else, just lay a plastic tablecloth (or if you need to spend money then Mothers Direct has a feeding mat for sale) on one of your normal chairs and get one of those portable booster seats with inbuilt harness from Kmart. We had one of these that we used for OS travel, as well as at home for sitting right up to the table
There's lots of ways to part with your money, and I'd save money on chairs to spend on other things!