Actually, the purpose of the GC89 device is to allow your laptop to surf the Internet using your cellphone providers network. I already have a phone for use for calling. I just need a means to access the Internet while I'm outside from the populous areas
You can use your cell as a modem to connect to the internet. Just take a look whether your phone support gprs (which in almost cases is true) and optionally edge or umts. Many gsm operators provide access to the internet even when you use their prepaid services. Their web sites:
simplus.pl you already know
I don't know exact prices, but I think that will be approximately 0,20-0,40PLN for every 100 Kb (sent + received).