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You will have better luck getting a detailed answer at pro forum - or just search their archive.
The price of print depends on your production costs. Since you take pictures for fun, then it will be just the cost of printing plus whatever you feel you deserve. In galleries, they normally multiply your expense by four, but again, galleries charge 50% commission.
I am not amazed by Costco canvas quality. They do not provide you with color profiles for canvas, and outsource printing to elsewhere.
Canvas on Demand does well with colors (and it is only $49 for 16x20 through Groupon) but their stretching is not consistently good.
Gallery Direct is another inexpensive place (if you search for their offers), quality is good and customer service is excellent.