In general, you get what you pay for.
I am a rep for a major sailmaker....
All the major companies build sails offshore now-a-days and have vaguely similar cost structures...
and, in general, you get what you pay for. You pay for the type of dacron sailcloth and the little details of construction.
For an inexpensive price, you'll get a sail make of inexpensive dacron, with minimum construction details.
For a middle price, you can get a sail made of lower stretch dacron, made with more reinforcements at slugs, clews, batten pockets, etc.
Every sailcloth manufacturer has a table showing which cloths are recommended for what size boats and the level of performance. First of all you want a cruising sail that is durable and doesn't require special handling. And you want it to last. And you don't want to pay a lot.
That means you want dacron sail cloth... probably. It's half the price of cruising laminates.
There are three grades of woven dacron cloth for cruising. 1. Economy cruising, 2. low stretch/high modulus, and 3. high-performance oriented wovens dacrons.
(high performance wovens are VERY expensive, more expensive than nice cruising laminates. So we'er going to discuss the economy and low stretch grades of dacron.)
Name brand cloth manufacturers (Challenge, Dimension Polyant, Contender, Bainbridge) sell dacron cloth in each category, in several weights.
All the cloths from name brand manufacturers will give you years of service if the correct weight is chosen for your boat. BUT The higher grades will hold their shape longer than the less expensive ones.
The difference in price is in the grade of cloth, not the weight. To go up one level in weight is maybe $50 more.
Upgrading to a high modulus dacron might cost $100-$200 more. And the sail will sail almost like new for years longer than the basic dacron.
I am very familiar with Challenge and Dimension polyant sailcloths; and passing familiar with contender brand.
Here's what the manufacturer's documentation recommends for your boat:
A) Good quality entry level dacron: one of the followng:
Challenge Performance Cruise dacron, 6.18 oz for cross cut mainsail. Dimension Polyant Coastal 270C or 270TNF (6.3 oz).
B) Better Quality, holds a better sail shape for more years:
These are the high modulus, low stretch cloths, made of more expensive dacron fibers. These cloths come specialized for various aspect ratios. Your Tanzer has an aspect ration of 3:1, which is high. We need a cloth engineered with a low stretch fill-thread.
Challenge 5.93 or 6.63. Dimension Polyant 230 SF (5.4 oz) with a medium tempered finish.
Construction details also are VERY important. But most folks don't know what to look for, because the details are subtle. A sailmaker who DOES include those features will be happy to show you. They make a difference in the shape of the sail as it ages.
You do want lots of reinforcement at slugs, leech edges of seams, and head/tack/clew. Cheaper sails scrimp on these details.
You don't need "blue water" features which generally add extra chafe resistance, double tapes, etc. You don't need triple rows of stitching -- you want triple-stitch zig zag stitching where needed, which stretches better than single stitch zig zag - which most sails have.
In general, you get what you pay for. Any body can buy sails in a foreign country and make inexpensive sails by using inexpensive cloth and building in minimal features.
Don't buy on the basis of descriptions like "coastal" or "off-shore" unless the sail loft gives you a list of what's included. And don't pay more for off-shore features unless you make long passages and/or sail in the tropics for weeks on end.
Hope this helps demystify sail cloth somewhat...
Hyde Sails of Northern California