I'm happy with the canvas we ordered last year and have been wanting to order another one. It looks like now might be the time.
For one week only (through 2/14) you can get 80% off the listed prices at Canvas People. I didn't check the shipping prices on everything, but it was $19.95 for the 16 x 20. (No coupon code is needed, just use my affiliate link above to get the deal.)
My advice on the size is to really think about it and measure it for the space you're putting it in. I wish I would have ordered a larger one.
The prices are listed below, but remember you'll have to also pay shipping.