... or take a chart and draw 50 and 100nm circles on it.
50 miles gives you roughly 2 x 30 minute out and return trips for the £100 burger
100nm (if shared with somone else) takes you further.
Or, do as I did in my gliding days. Work out a mini-triangle of total length of 100nm.
All of this will show you (and depress you) how far you can fly against your budget