That is the correct range of weights - there is no "absolute". Expect the quotes are for different fabrics in the same price/performance range. There is a wide choice of fabrics, cuts, construction and if you are investing in a new sail then suggest you read up on the range of choices before making a decision. Most of the bigger sailmakers have useful guides on their websites plus you can always ask why they are recommending what they are quoting you for. A good thing about using a UK sailmaker is that you can have a meaningful dialogue with them to be sure that what you are buying meets your requirements.