Oh goodness me - some people have no vision! I think it's fab - love the fact that you are using somebody's own fingerprints to create a piece of wall art and it looks great. Ignore the business bods ... they probably aren't your target market! You are playing on sentimental as well as aesthetic qualities, there's a great market for that.
We sell silver fingerprint jewellery - pendants/cufflinks/charms etc - and they are expensive in comparison to ordinary pre-made charms but people expect - and are prepared -to pay a premium for this. It's a popular seller for us and customers love the idea of having something created especially for them. You can't get that in Tesco or Debenhams, it's what we specialise in.
In terms of cost, without touching/feeling it it's hard to guess at a price; ask what you feel you need/want/deserve for creating it - people will soon let you know if you are way off the mark, and it depends on how/where you are selling.
I like it - it's a fab idea. Well done!