I go back and forth on how to manage people who contact me via the Internet (who aren't customers or referrals) seeking out quotes for upgrades.
I find that if there is no prior connection (they aren't referred or haven't seen me speak, received a newsletter or found some piece of life changing info on my web site) that 99.9% of the time the quote is nothing more than a request for a third bid.
It's even worse when they want it in writing and to have it binding. All for free.
What I'm doing (and have been for a while) is to use a list of services that I might perform (everything I do is fixed fee).
For upgrades I figure out about what each level of upgrade would price out as (I just go through past upgrades and average out what people typically pay).
Then I give that number as a fixed ""starts at"" price.
Then if the prospect wants a written project plan (I would not use the word quote) there's a fee that I charge and specify that it's rebated against the final invoice.
It's a bit crude but it's one hell of a lot easier to have some standard prices rather than try to remember what you quoted some anonymous web visitor 11 months ago via a web inquiry (they all seem to take 11 months to make up their mind then come back during your busiest season asking if you can start next week).
Tip: If you are fixed fee billing - then I believe your verbal/informal quotes should always use wording ""starts at ... "" -- to avoid locking yourself into a formal price before you have enough detail.
Tip #2: A large number of Internet leads are sandbagging you. They have a secret that they won't disclose (customizations, screwed up data) and it's up to you to find the secret ....