My company specializes in acquiring domains. Looking at the whois record for Dost.com, it appears to be the owners last name, and it's been registered since 1995. There is very little chance they will sell cheaply. The .net and .org were registered in 1997. I'd guess at least $5k US for the .com, possibly that much for the .net or .org too.
According to Google translate, Dost means "enough" in Czech and the .cz was registered in 2001.
If you don't have a big budget, Evotion's advice to combine other meaningful words with "dost" is the way to go.