Here are some typical sector costs for a low-cost config (149 seat) 737 - the example is an approximation of an easyjet operation:
GLA-AGP one-way
Fuel: 1370
Maintenance: 812
Landing, Parking: 261
Airport Infrastructure: 33
Handling: 449
Navigation: 1267
Crew Allowance:67
Contingency: 213
Crew Salaries: 666
Lease: 1066
Insurance: 133
Overheads: 1118
Total: 7455
The above assumes full airport charges at both ends of the route and that the passenger charges and taxes are added onto the ticket on top of the fare.
At a 70% load this flight would require a contribution of £71.48 per passenger on average. This will be a combination of the fare paid plus any bar profit (usually £3-4 per pax).