I am a current BA pilot, so I can help you understand a little of the salary in BA. Every mainline BA pilot will join the BA payscale. This currently has 24 increments (one for First Officers and the other for Captains). In the past, SSP pilots or cadet pilots would join on the reduced salary, but every year will get an increment to their basic salary (as all BA pilots do). These increments are in addition to negotiated pay-rises, such as the one given to all pilots earlier this year.
The increments for cadets will increase to meet the equivalent Direct Entry pilot payscale by a certain time (5 years on the old SSP scheme). By your 6th year you were on the same paypoint as any pilot who had been in the company 6 years (58.663GBP on Short Haul or 62,266 on LH), regardless of being a cadet or direct entry. Hence in 6 years time you will be getting a lot more cash than a SFO at EZY. Don't forget, most low cost airlines do not have increments. The salary you join on is the same until you get promoted. The allowances are not all subject to tax either, so the 'real' salary is greater.
If you can get through BA selection, you would be mad to turn down the offer. In the meantime, you need to concentrate on getting yourself through selection.
Remember never to become a pilot to become rich. Those times are long-gone. If money is your motivator, you need to look at a different career.