@matigo Yes, you have the advantage of already being an expert in the domain & your company’s systems. That does save time.
On the dishonesty front, I’d recommend looking into value-based pricing. It’s not about “how many hours did it take the dev team” - it’s about “how much do the clients value having it done earlier” or more sharply “how much money is left on the table each minute without this software up and running”. From that POV, throwing someone just a week’s salary for something turning profits of several million a year sounds rather unequal, no?