My situation is that I have agreed on a per-project proposal with the client. The proposal is vague, but still names functionality in a way that can be argued as to whether it's included or not, while leaving some room for interpretation. I originally pressed as much as I could to get a per-month contract, arguing that the project is mostly non-predictable, but the client refused. Being a small company, I had to fold and signed a contract on an estimate based on my group's estimations. At this point we have reached completion on about 85% of the features (we think) but we ran out of budget. We have been working for almost two years with this client in previous contracts, and we have delivered a good product that they are happy with, so we have a good standing relationship.

More info: -There has been a bit of scope-creep, but I don't think enough for me to hide behind that argument -We've been delivering partial releases about monthly. -We don't have systematic user-testing in place.