The best software for this kind of job comes with arms and legs attached -- it's a composer in the flesh. There are so many people out there who do a nice job composing -- students and professors in a college setting who might very much like to work on such a project and they won't charge much more than some of the software packages you've been discussing.

Drop by the music department of a local college or university and ask around. Chances are most of the composer types own their own software already and they know what to do with it and they can bring a large understanding of style, history and and music theory to the task. They also provide another soruce of creative energy that you can draw on in your work and that's the best benefit of all.

I'll agree you don't need the advanced versions either, but I'm also not a Cubase fan. Having all of them (Logic, Cubase, Reason, Finale, Sonar), I'll take Sonar 5 in any of its flavors. I have the East/West library as well, it's quite good. Another to look at is the Symphonic Fields Forever libe, and if you can find it (long out of business) the "Speaking in Strings" library.
All of these packages are for if you are a musician, which hasn't really been clearly stated. If not, ACID with any of the orchestral packages is so easy to use, even small children can make very impressive scores with it.