Hi,
I've written something similar for myself. When I scan a stock item, I generate a label and send it to a GK420D. The thing I wrote was in PHP, but I''ve made a very similar thing with an interface in Python - that was an app which allows me to record the weights of goods when I receive them (by putting them on a set of USB scales and scanning the barcode).
So I'm sure I could mix those 2 things together to create the kind of app you need.
The only thing I'm not sure about is "label designer" - what do you mean by that?
Anyway, what you're asking for seems to contain a lot of things, and I know your maximum budget is 30 Euros, but it would take quite a few hours of work to achieve what you want.
Just send me a message if you want to clarify what kind of thing you're looking for.
Thanks a lot,
John