On eBay Sure Electronics offers an 8x32 LED matrix, single color, for $10 postage paid, tax free, from Hong Kong. Up to 4 of these can be chained together for an 8x128 (or 32x32, etc.) matrix under the control of a single MCU. It takes 4 I/O lines to drive the first one, plus an additional line for each of the additional 3 boards.
This project gives complete C code (ICCAVR V7, regardless of the V6 shown in the summary) for some routines handy for driving up to 4 boards as a message unit (placed end to end). A mono/proportional font is built in, plus bit, column, and multicolumn reads and writes.
To find these boards on eBay, search for the term "0832" and look for the free shipping listings.
The zip file includes a PDF write-up, three C source files, and two header files. The full ICCAVR compiler is available for a free 45 day demo, after which it reverts to a non-commercial, size limited but otherwise unrestricted version.