so, it sounds as though maybe you don't have a complete understanding of how chip burning works.
there are some good articles on it, but as a brief overview, there are a number of things you need:
1) the bin file. this can be had by reading the chip in your car (which, in most cases requires you to de-solder the chip and put it in a PROM reader/burner), or this can be had if you know the part number/code of your chip and you download it.
2) the editor. you can use GMECM Edit to edit the chip, but you need the ECU file (which is only a "description" file) to edit the mask (which you say is $88 ). You can get this from various sources, include
www.diy-efi.org/gmecm/ FTP, or by looking around at
www.thirdgen.org. There are a number of resources for ECU files. Some are better than others. In some cases there are multiple ECU's to choose from for a particular mask. Some are better than others.
3) the burner. once edited, you need to burn it on to a new chip (you can't burn onto the old one). This, again, requires you to de-solder the chip from the CALPACK.
if you're not comfortable de-soldering the chip, or intend to one day put things back the way they are stock, you can use one of the adapters by Craig Moates.
www.moates.net. Thats what I do.
as far as getting help on this, the message boards at
www.thirdgen.org are a good starting place. read the archives, then ask questions if you're still unlcear.
theres a bit of a learning curve when it comes to DIY PROM burning, but once you have everything in place, its pretty simple.