For an extra £25 for 6 months (on top of the £25 for a regular subscription) you will get, in Peter's own words, "access to many of the tools I use to develop the ports in a Unix cross compiling environment, and support for their use in your own porting". More tools as they are developed are promised, as well as help for general porting problems.
Also announced is a way to pay for your subscription through PayPal; although you can still pay via cheque as well. Don't forget that for an additional £25 you can get a subscription with Browser Support - and who doesn't want to see a decent browser ported to RISC OS?