
Sabre Wulf is a port of the Spectrum game for the 99/4a, 32k memory expansion required
The programmer has identified this project as a labor of love for which no profit is generated - and for which he receives no payment
In other words, the software is free, the price reflects the manufacturing and selling of the physical cartridge alone. There is a manual in pdf format available at the link below.
For more information on the development see the atariage forum: