[athenot]

If anyone else finds themselves in this position, don't ever entertain fixed-price bids unless you're absolutely desperate for work. Instead, insist on an hourly rate (at approximately 1.5x - 2.5x market value). You're essentially an expert consultant brought in to address a very specific need that the company has yet doesn't want to invest in mastering themselves.

Reframe a fixed price as "this will be X amount of hours". Invariably, nobody knows what kind of "gotchas" will be encountered during dev, and with fixed price, you're absorbing that risk yourself. As an hourly rate, that risk is borne by the client. This also applies to shifting scope; if the client shifts scope mid-way, they will bear that cost in an hourly setup instead of you.

[sph]

Fixed prices are always an incredibly bad idea, unless the price is based on your (possibly unique) expertise rather than time involved.

If you can bill $1M for a project because you're a worldwide expert, do so, otherwise bill by hour/day/week because you should already know that deadlines will be broken and the spec you are given when you sign has nothing to do with actually is required to ship the product.