Vinyl is the most unsustainable material you will find, and unfortunately it's everywhere. From home goods to fabric, vinyl is common simply because it's cheap, easy to product, and durable. Vinyl is make from ethylene (found in crude oil), and chlorine (found in salt) When processed, both the substances are combined to form Polyvinyl Chloride (PVC) resin (Source: http://www.whatisvinyl.com)
PVC is a very toxic plastic that releases chemicals throughout its lifespan and because it is a plastic it is not biodegradable though it can be recycled.
Most of the items that utilize vinyl can be very affordable simply because the fabric itself is affordable and common. If you are trying to be more sustainable, be aware that any item with a very low price and says PVC or synthetic materials could be vinyl. It never hurts to ask a company what something is made of so you can be more aware of what you are buying.
Polyurethane is similar to vinyl but more sustainable in the fact that it does not use solvents and harmful chemicals like PVC and some of it's materials are biodegradable. How it is manufactured can also make it greener. The polyurethane that I use from Ultrafabrics recycles all its waste and has certified its materials and production with the California certification program making it Green Guard certified and uses no toxic or cancer causing chemicals.
Polyurethane is made from a polycarbonate and typically has a rayon or felt backing. And can cost as much as leather based on the quality of the fabric. Typically you are looking at a mid range to higher cost item utilizing this material. Stella McCartney uses this material for most of her vegan fashion products.
The newest, latest and greatest faux leather option on the market. Piñatex™ utilizes the once discarded pineapple leaves to create a soft vegan leather. Utilizing a once wasted product makes this material sustainable and a great vegan choice. However, this product is not completely biodegradable and there is some care to this product.
Visit http://www.ananas-anam.com/pinatex/ to see their manufacturing process.
Cork is the most sustainable material out of this bunch. Cork is found on the Cork Oak tree typically found in Spain, Portugal, and France. It takes 20 years before the trees can have their bark stripped to make cork leather but the tree isn't harmed and can be re harvested in 10 years. Once it is stripped, the cork is boiled and shaved into thin strips and binded typically to a fabric baking. It's soft like leather and naturally resistant to water. Cork ranges in prices based on the quality of the material. Most authentic cork products from Portugal are priced similar to common leather bags.