Whatever you do, do NOT go to your local antique store and buy a crock for your starter. Most crocks from the 1940s and earlier contain lead. You can be sure your starter will absorb any lead or trace metals that may be in the crock. So unless you know the date of your crock, beware!
I think the best deal is this 1/2 gallon jar for $11.99 from Marshall Pottery. Of course, you have to make your own wood lid...or find a round plate that fits securely on top. (Preferably a heavy stoneware plate.)
One of the many things in life I don't understand is that there are companies online who sell sourdough starters in jars like the one pictured above. Yikes! Your jar or crock should have a lid with an easy or loose fit to allow some "off-gassing." In the above jar, the building gasses would blow the top right off!
However, if you want to use that jar without the rubber seal, that will be fine. Just make sure there is a little space between the lid and jar. (Actually, the space between the lid and jar in the first picture above is too wide...but you can find jars that have a closer fit.)
I bought the above jar at the thrift shop. Please don't ever keep your starter in a jar like this...the lid is clamped way too tightly. This jar must be intended to store dehydrated starter...more on that later.
Le Crueset makes this nice 2.25-quart stoneware crock for $20. It comes in many colors. You may be able to find a round cutting board to use for a lid.
King Arthur Flours sells this 1-quart crock for $21.95. Lehmans.com sells these 2-quart size bean pots that would be an excellent choice. (I love the blue color!) The blue pot is not sold in the catalog, so order the 2-quart brown pot but be sure to specify the blue pot.
So have fun looking around. I am on my third different crock, so don't be surprised if you change your preferences from time to time.