It is very, very rare for a quote to change after you've entered in all the details, but here are a few things to keep in mind.
If you get a Quote without designing a shirt, it is based on the exact details you entered in the Quoter. For example, if you quoted just size small shirts, your quote will change if you add XXXL shirts. If you quoted based on white shirts and then switched to red, the quote will be higher on red.
If you get a Quote inside the Design Studio, your quote is based on exactly what you see on screen, and what you've entered if you uploaded your own artwork. For example, if you uploaded artwork and selected FULL COLOR, it may quote higher than if you just select one color for print. If you get a quote and you don't have a design on the shirt at all, it will quote you on a blank t-shirt.
Please call us if you need an official quote emailed over, and we will be happy to assist!