The Better the Requirements, the Better the Quote!
Are you guilty of asking a vendor how much something will cost, without giving them sufficient requirements for the project? Maybe you feel vendors should be able to provide a "ballpark" estimate from just a summary of what you need? The danger, of course, is a quote for services that isn't even close, or worse yet, a quote for a solution that doesn't match your actual underlying goals.
If you aren't sure what is really going to be required, but still need to obtain at least a range of fees that might be incurred, start with a conversation with the vendor where you describe every aspect of the project you do know, then identify any "gray areas" you aren't sure about. This will help your vendor/partner hold more productive internal discussions with their broader team of design and development experts to reason through your requests, then respond with questions you can take back to your team for clarification.
The resulting "second round" of detail always proves enlightening. And whenever possible, a call directly between your internal requestor and your vendor/partner is ideal for these kinds of high-level discovery efforts. It is often the case that a direct conversation yields a totally different outcome than what numerous emails would have achieved. Sometimes the project takes another path entirely than what would have been quoted had you not taken the time to engage the parties in some good 'ole fashioned verbal communication.
You may have to do a bit more homework on your end and coordinate a few more web meetings, but the more detail you can collect before requesting a quote, the better the estimate will align with the requirements, and ultimately the better the outcome will be should you move forward with the project.