Can you show your working please?
£9.50 average ticket cost X 23 games X 8000 = £1,748,000 - £300,000 (ticket revenue from Sixfields) = £1.448m extra ticket revenue.
I forgot the exact figure OSB quoted but was roughly £1m loss + £1.448m extra revenue = profit of £448,000 or "about half a million".
Figures are rough, you could argue on a lower average ticket price, or a higher or lower average gate, or the odd cup game. But on average it seems reasonable to me.
To flesh that out a bit: you'd have to either cut the ticket cost by an average of £3.80 or cut the average gate by 2056 (to less than 6k) before you made a loss (or some variant of both).
One sell out cup game at the Ricoh, would make roughly £300,000. For comparison one sell out game at Sixfields would make about £73k on last seasons capacity (both of those at £9.50 avg price but in all likelihood it'd be higher for that type of game).
Fine if you believe losing millions for the years we're away is worth the risk on getting a better deal/new ground. But be aware that that is what you're saying.