In short, you never coded anything, so you must rely on a developer...
Using the Host company developer is not the best option!
You pay your hosting service to "host" your site and hold your domain. Nothing else.
THEN, you code your site or you use the services of a developer.
Since your site was already up in the past (and, I suppose, working), it should only be a matter of recreating the databases (if any) and uploading the scripts.
The cost would obviously depends on the number of files, folders, sub-domains, databases etc, and the set-up made by your previous coder (constants, passwords etc)
If the code was badly written in the first place, it could be the hell of a hard work to clean it up!
Hard to say what is reasonnable or not!