I'd like to mention that canning jars can be used for sous vide instead of bags. There are standard sized
and wide-mouth sized
attachments for FoodSaver vacuum sealers the cost is around $10.
These jars are designed to be used in preserving food with both the water-bath canning method and the pressure canning method. They can easily withstand the temperatures of an immersion circulator, and, they hold a vacuum very well.
The jars themselves are obviously BPA-free. The lid is two parts: a metal retaining ring that is used for safety, and a metal lid that has a coated rubber ring fused to the underside. The underside of the lid has a very thin plastic coating which does contain BPA. However, since safe sealing of the jars requires about an inch of head room, or more, between the food and jar rim, the food will never come in contact with the lid. If operators are careful to not tip jars on their sides, exposure to BPA should be extremely limited.
For home canning, cooks are warned to discard the lids after one use. This is to ensure good, safe results with lids that are expected to hold a vacuum seal for a year or more in storage. For sous vide, I have been able to re-use lids for quite a while, I cannot say precisely how many uses. I wash them carefully by hand never use abrasive cleansers or abrasive sponges on them, and sanitize with a non-corrosive sanitizer. The main concern is how well they maintain vacuum. I check my vacuum before cooking, and before serving. Obviously, if the vacuum doesn't exist then I'm not accomplishing what I set out to do. Your results with lids may vary.
For several years now restaurants have been serving items in the jar itself, making plating easy. They provide structural support not possible with bags, so, layered dishes are possible, among other things. I have experimented at home with sauces, vegetable gratins, and scalloped potato variations in them.
In the US, they are available in many sizes, from several manufacturers. Common sizes include: 4 oz, half-pint, pint, quart, and half-gallon in regular and wide mouth versions. (These are the common names for the jar sizes as they appear on manufacturer labels, I know that the terminology isn't consistent.) Half-pint and 4oz jars are also available in a quilted jelly version, which has slightly thicker glass and an attractive outer texture. Boxes of jars generally come packed with one set of rings and lids for each jar. Extras can be purchased separately as sets of rings & lids or individually.
Jars are available at ordinary grocery stores, mass-market big-box retailers, some restaurant supply retailers, and some hardware stores. Prices vary by size, but most are available for under $2 per jar.
I hope this helps some of you get started experimenting with sous vide in jars!