Because the bid in not specific enough to make a valid offer, we stated our minimum price for the work we think might be involved with the project.
We from @Quest WebDesign have extensive experience with Mambo, we build over 50 sites, many modules/components/mambots and have experience working with both non-tech and tech-savvy clients.
If you require, our hosting solution even comes with our custom-build auto-updating Mambo installation.
Note that we fully document all changes we make to exisiting (open) source code. We can communicate via phone/email/IM/skype/etc. Payment via invoice/paypal/GAF/etc based on a fixed-price offer or budgetted feature/change requests.