No: I meant, if you pay, you pay a total of £250.

i.e. a slightly clearer statement of my imagined setup is this:

Omega flips a coin. On tails, he asks you if you'll pay £125 now, knowing that if this is day 1 he'll wipe your memory and ask you again tomorrow.

On heads, he simulates you and sends you £260 if you pay.

There is never any money paid to non-payers.

(Basically, the only difference between this version and yours is that both paying and not paying have a return that is £25 lower than in your version. That surely shouldn't make a difference, but it makes the problem go away.)

• Not paying always gives £0.
• Precommitting gives a return of 0.5 x £260 + 0.5 x (-£250) = £5
• By your logic, at the time of the decision, return is 1/3(£260-£125-£125) = £3.33

Isn't that correct? I admit I suck at maths.