IsoDraw With CadProcess (3d file manipulation add-on) its a little over $11,000. (I am sure it is much cheaper without the 3D component, but I don't have pricing on the isodraw by itself. Pricey, I know. Very worth it though. Not that I recommend it, but there are other ways of obtaining a copy, but if your company is needing something they should be coughing up the dough to get it. You could use Adobe Illustrator for around $900.00, but its not made for isometric technical illustration, and its a little like using a round orange into a banana slot. It'll work but there will be a lot of extra work involved.
I have also heard there is an expensive add-on for CorelDRAW. And it must be at least moderately acceptable as I have seen some low-end illustration job ads call for it. I have not used it though, and absolutely ABHOR corel's other products, so honestly, personally I would be hesitant to even bother with it baring a no-other-options situation.
But saving the best for last, AcdSee has got a new technical illustration program. I have used their photo software for years and absolutely love it. The program is $800.00. But they have bundle deals on their site all the time, so look for those, and if you call ask for a deal. The best part is they have a trial period so you can test the software. I have not tried it yet but am eager to.