There is a lot of discussion at the moment within the TA about pay and Cost of Living Increments (CoLI) which i would imagine is also relevant to the RAuxAF. Basically this pay increment is supposed to ensure that should you be called up/volunteer to do Full Time Reserve Service (FTRS..I believe the term is the same for all 3 services) alongside the regular forces (which I would presume is what happened with Regie) the MoD pays you an "X"factor to ensure that you can continue to meet your financial commitments if you have to take a drop in pay from your civilian pay to forces pay.
However, and here is the rub, the CoLI is linked to your military rank on the assumption (often wrong) that your position in civilian life/work mirrors that in the forces. What is overlooked, especially in the TA, is that a lot of soldiers have well paid jobs and get involved with the TA for a bit of fun. The Honourable Artillary Company have suffered in this respect immensly with soldiers who work in the City on $100K a year salaries having to cope on $17-20K (sorry, no pound sign on this computer) as they get called up for short periods working alongside the regs in places like the former Yugoslavia, or large ex's like Oman. Just because you have been called up for 3 months does not mean that your financial obligations at home stop, and many guys in the HAC have been left seriously out of pocket.
When considering working with any of the reserve forces it is important to understand not only what the reserve commitment might mean in terms of being called up, but also how likely it is that you may be called up (certain areas of the TA such as the medics, signallers, RLC mobility specialists, and sappers seem to be in constant demand) and what the financial implications may be if that happens. While many unit commanders are sympathetic, if you are needed and not enough volunteers come forward you may end up being drawn through a "lottery" system anyway.
I would not wish to put anyone off joining the reserves, but these sorts of issues very rarely get discussed when you sit down with the recruiting officer at the unit you wish to join.