Nice though they are, prints like this reproduced in modern times for sale in museum shops don't have a great resale value. Although they may originally have been quite pricey, if nicely framed they generally resell for anything up to about $50 (unless they're from limited edition runs). If you Google for eBay listings you'll see both of those prints offered at a variety of prices.
One eBay seller has the "Old man and Child on Buffalo" print listed at $150 but I think that's a highly speculative price which won't be realised.