don't do same mistake as I did once, buying cheap (on eBay in my case). turned out to be a bit of a disappointment. Later on I purchased a similar canvas print from www.mcanvasprints.co.uk/, which didn't cost much more, but the result was so much better.
the trick is to look for information on their website on how they make the prints and what materials they use. you don't necessarily have to know what they are talking about... it is just that they mention it. if they do mention it, then they are less likely to be hiding something from you.