Yes, you can calculate hourly costs for a major project by keeping track of engineering effort...but what does that have to do with old players rejoining?
Okay I admit I wasn't completely clear with what I was talking about. There is a developing cost for new content, right? Because players value content differently, and some content will have more of an affect on the players than other content, it is possible to calculate how valuable different content updates are. There is definitely content in RS that is rarely used, and so the costs of developing that content did not bring back worthy gains.
Just looking at the main RS page, I doubt the sinkholes content is going to spark huge interest in retired runescape players, it's not going to suddenly bring in a lot of new players. This 07scape has created a lot of talk, and a lot of talk from retired players who express interest in returning, so the developing costs for 07scape is likely to be a lot more valuable than just your average RS update.
First, the reward is large, I won't deny that, but the risk is just as, if not, larger.
However, I prefer to take a more conservative approach to estimates, and 150K players seems way too optimistic. I'd be willing to go as high as 20% of that number, which is a crazy high ballpark, but not more. The reason I say that is twofold - you can have a large number of players voting, but that doesn't mean they'll follow through with it, or be willing to pay the extra cash for it month after month. You'll have a lot of people just drop off the bandwagon and find something else to do/complain about.
30,000 players is optimistic, even for me, and that's only if everything goes flawlessly. You would have to convince not only the players that voted for this to pay their dues, but also those that abstained, as well as those that are optimistically ambivalent.
The catch here is keeping them. You can expect it to be as jam-packed as RSC was when the floodgates were first opened, then you can watch the numbers trail off by a lot when they realize that it's not nearly as technically advanced, rewarding (from their perspective), or enjoyable (again, from their perspective) as RS proper.
My gut tells me that, regardless of the tier, you'd get 5,000 dedicated players. You'd also get 10,000 enthusiasts; people that'd be interested in the game just as a fleeting fancy. Well, $225K isn't much to sneeze at, but it isn't enough to cover all of the costs to make this happen. Jagex would be swallowing the costs of the project for $5/mo, which - with that level of interest - would barely pay for the dev needed to maintain it in a month.
I'm not going to pretend I can estimate how many people can play, but I find your 5k dedicated and 10k enthusiasts to be quite pessimistic.
Despite the hype, you have to lower your expectations by quite a bit. For every ten people that chirp up, maybe 2 or 3 of them will actually follow through with it. Even less will continue to stick with it.
Developing software just isn't cheap. No matter how you slice it, it still costs a lot of money. And again, I'm only talking the personnel costs here - if we were to talk archiving/SAN, we'd be adding on another $30K easily - and that's for the hardware alone.
Yes developing costs are expensive, but the content has already been developed! Suddenly this huge development cost has disappeared. It will only be a small team to basically set it up, yes there will be a tiny bit of development, but compared to the actual content, that is ready to go. Also, you seem to be forgetting more overhead costs that don't have to be considered, Jagex already have deals with server providers and everything for current RS, will these current providers give away the potential to get a lot more business from Jagex? Of course not, there will likely be cheaper costs since Jagex will be an on-going customer.
Development costs are expensive, but the content has been developed!
Overhead can be expensive, but most of it has already been covered!
The main costs involved will be the running costs, which is relatively cheap. There will be a bit of development overhead to get the servers ready and started, but than other than that there isn't too much more, especially compared to main RS.
So yes, an individual looking at the costs of running 07scape will think it sounds expensive, but for Jagex it will be relatively
cheap (not to mention the likely potential gains).
And to finish off, if this 07scape turns out to be a huge flop and waste of time and money, Jagex will brush it off and move on. You wont notice a thing (if there was real risk in this it wouldn't be given the chance).