Stainless steel is more expensive than some other material because stainless steel is corrosion-resistant. It does not corrode, rust, or stain as easily as other materials. Stainless steel is an alloy that by definition must contain at least 11% chromium.
Stainless steel comes in different grades and surface finishes.
Stainless steel grade ranges from the 100 series to the 600 series depending on their alloy composition. Then there is the type 2205 grade (known as duplex 2205). At the center of the range, you have grade type 304 which is the most common stainless steel grade.
Surface finish for stainless steel ranges from No. 1 finish to No. 10 finish. They can be brushed finished (No. 4), satin finish (No. 5), matte finish (No. 6), reflective finish (No. 7), mirror finished (No. 8), bead-blast finish (No. 9), and so on.
Stainless steel pipes can come in various diameters typically from 1/8 inch to 96 inches. They can have various wall thickness, giving you various inside diameters. Although not often used, stainless steel pipe can be made up to 3 inches thick.
Stainless steel pipes come in various lengths ranging anywhere from 10 feet to 120 feet. They come in different "schedules" such as schedule 40, 80, 10, and schedule 5S.
Stainless steel pipe have a maximum temperatures and pressure ratings. Typically 200 psi and temperature from 0 to 250 degrees Fahrenheit.
They usually come unthreaded so that you can thread them to your specifications. Some manufacturers will perform specialty testing such as X-ray and hydro testing.