The only upgrade to a current version is CS6 or CC, which is subscription. You can find old versions on eBay, but beware as there are a lot of counterfeit copies there.
CS3 had the worst version of Bridge.
As a business, and with the sort of work you are doing, I would try to get the $10 a month Photography deal. You would get tax breaks on the cost of Photoshop, and be able to produce some very cool designs with ease.
Look through this long list of tutorials.
Scripted patterns and fills
Any of the 3D tutorials
The 'Painting drawing and type' subsection.
And anything that looks interesting. The difference between Photoshop CC and the very old Version 7, will astound you. Some of it will take some learning, but this forum will always be here to help if you get stuck.
I agree with Trevor.
If you choose that option, before you sign up, make sure your current hardware and operating system can run Photoshop CC and Lightroom 5
e.g. neither version will run on Windows XP or Mac OS X earlier than 10.7.