Its a tricky one, you could work for x amount of hrs one week and get 2 templates done, then the next week work x number of hours again and not even get close to finishing one template. It is very hard for an employer to really pay you on a time basis as its hard to judge what the designer can output in x amount of time. Plus its not even a full time position so thats another negative for the employer, the fact that it is your secondary function means you may not have the same focus and attention span or creativity flare as someone working full time or at least using this work as the primary work.

I think Robsons suggestion is probably a wise one, at least until you decide to go full time if thats something you think you will ever do. If you do a design a week im sure you will be able to sell it on forums and reach your goal of £100 with ease.

The above was just might personal suggestion and i wish you luck trying to find an employer that is looking for someone like you.

Anjam