For a custom software that will likely take a year or more to develop, how would I go about determining what to charge as a consultant? I'm having a hard time coming up with a number, and searches online are providing vastly different numbers (between $55/hr and $300/hr).

I don't want to shoot too low because it's going to take me so much time (and I'm deferring my education for this project). I also don't want to shoot too high and get unpleasant looks and demand for justification. FWIW I live in Canada, and have approx. 10 years of development experience.

I've read the "take your salary and divide it by 1000" rule of thumb, but the thing is I don't have a salary. Currently I'm just doing fairly small programming tasks for a friend who is starting a marketing company, pricing each task fairly arbitrarily. I don't know what I would make over the course of a year doing it, but it would be incredibly low.

My responsibilities for the project would be the architecture, programming, database, server, and UX to some degree. It's going to be a public facing web service so I will also need to put a lot of effort into security and scalability.

Any advice or experience?