Hi, I'm in autoID bussiness for almost 10 years now and my daily job is development/support of applications for exactly same mobile barcode terminals, so I've access to MC9090 which is quite similar to yours MC3090 (I've worked with this terminal also in the past), so the quality of the application and your satisfaction is guaranteed. I've coded similar stock taking applications before.
I'm coding everyting in plain and clean C (well documented) so it's quite portable and without any dependencies nightmares. As a bonus I'll provide you the installer of this application also, so the installation of the application on the terminal is plug&play also.