Would this not be just a switch part and relatively simple to do perhaps (prolly a breaker part obtainable), relatively cheap depending on the parts cost required. That said I think there are some complexities behind how the Fiesta heater might work and I am sure someone will be around shortly to provide more details but by not working seems to suggest that you mean that certain positions mean no blower, which might suggest the switch itself.
Maybe it is even "serviceably repairable" ie a bit dirty on the contacts or something, if you take a look at it in more detail by removing plastics carefully. That said should be a very quick fix from an honest garage and I'd be surprised, it not appalled, if quoted much above £50.
I'm quite up for a challenge so would probably try and fix it myself certainly on something this basic sounding, dunno about you.