Yes, it does, although the price can actually change while you are in the process of buying, though of course this is just a minute or two window, but it did this to me on my last purchase, but the price only rose a buck or two so I didn't freak. Anyway, once you complete your purchase/sale, the price is "locked in", yes. I've had very good luck with coinbase, although I wish I didn't have to wait so long to get my coins, but I don't have a credit card to do the last step of the verification. I wish that all these businesses could see that people like me are trying to get away from institution-controlled things like credit cards, rather than using them, but I understand they are trying to protect themselves from charge-backs and such things.
Good luck.
Thanks I made my first purchase yesterday it said could take 4 days but now says end of the 26th maybe because of the holidays?