If you just want to maintain an already shave ready razor a barber hone in the $50.00 ballpark .... or less... will do fine. You'll have to look in the SRP classifieds, ebay, flea markets or antique shops as they are no longer in production. You could also go for the Chinese stone at Woodcraft for around $20.00. It is for finishing but would probably keep your shave ready razor going.

If you want to buy old razors and hone them from scratch to shave ready a 1k, and a 4/8 Norton would do it but you'll also need a flattening stone or you'll have to work with sandpaper. That is doable but in the long run the flattening stone will probably be the cheaper way to go. To hone razors with any kind of efficiency and consistency there are a minimum of tools you'll need.