In addition to adding the "required bank +1 to each object" you should have "required bank + best object". Most people buy their stuff one at a time.
You should add the upgrades which are click dependent. The "big cookie" ones like "plastic mouse" and so forth are quite easy to calculate - just make an input for how many clicks per second the user is expecting and then you get a cps rating for them. To make it more accurate and to account for the golden cookie upgrades as well would be a lot more complicated but maybe interesting to model: the user can estimate what % of golden cookies he expects to catch, and when does he think he's going to click the big cookie (for example: "only during click frenzies").
Issue #17 resolved