see, the problem here is that based on the answers I saw in this thread most people that posted smart ass comments have no clue about what they're talking about. It's not a coincidence that Grouchy Admin and Woj gave the most valuable input so far: they know their shit.
If you're upgrading from 1.5 to 2.8 there are many variables that can go wrong. Non working plugins is the easiest one. Let's follow with database issues, database tables left by plugins that won't work, themes with deprecated tags (hello!!! 1.5 and 2.8 tags are quite different!!!!), possible javascript issues and so on. It's evident most people here thinks they just need to upgrade automatically (which, of course, won't work) and that all versions between 1.5 and 2.8 didn't even exist. Let alone if you were already attacked and you still have vulnerabilities in your server.
In short, the question is: can you pay it? if answer is yes: will it save you a headache? will you continue to make money? is it worth the time you'll save instead of having to learn things you'll ever need in the future? can you afford to let newbies handle a site that makes you money? Consider all that, ask for guarantees and references and then act accordingly. And don't pay attention to GFY funny guys, they won't save your business, they can't even save theirs!
PS: the above being said, unless your site is a real mess, the price is a little high. If your site is a mess (which is quite possible since you were attacked and already had a failed install by your server guys), and they can guarantee results, the price is really low
PS2: see a list of deprecated tags at
http://core.trac.wordpress.org/brows...deprecated.php
PS3: see what it takes to upgrade 1.5 to 2.0 at
http://tamba2.org.uk/wordpress/upgrade2two/ Then think this is the easiest one (1.5 to 2.0) 2.8 has even more changes