Can you enlare it in sections on the copier (say 4 quadrants) and then overlap and tape them together? What didn’t you like about your effort with the copier? What about giving someplace like Kinkos a shot at it?
Kinko’s should be able to do that for less than five dollars. I take things in for work all the time. I put my pdf files on a usb stick and they blow them up and print posters for about three dollars. It’s quite nice really. I have also sent them files by email before.
Be sure to give them a call first to make sure they’re comfortable with your file type.