They are tailored to the engine so unless it was for a 1.9 TDI with exactly the spec of your Fabia you could do more damage than good
I see what you mean about spending money on the car, maybe a £399 remap is ott, you could try a tuning box although I haven't seen them as cheap as £75.... but at least then when you part company with the car you have something saleable to get some pennies back
That looks like a good bet, I very much doubt it is as effective as a full remap but then for £80 you can't complain...