Hi Ronfar,
I agree with both Ironlords and Oceans. I have a fair number of antiquarian books, they have always been a passion of mine. One thing that I have learnt over the years is that true antiquarian bookshop owners are generally keen to help as they are generally passionate about books, and also love to come across something new to them and maybe to the market.
I personally wouldn't pay for an appraisal just yet... try to get a couple of free ones, and if you are able to identify it and are given a rough value, then that is the time to think about taking it further. But there are some sharks out there and so if someone tells you that it's only worth $10 and then offers to take it off our hands, then beware. Look up Antiquarian Bookshops in the Yellow Pages/Online .. send your pics and description... some will respond... Take it to the local shops (if there are any)
If, as you say, the drawings are original and not prints (which they certainly seem to be) then yours is most definitely a unique book. Unfortunately unique does not always equate to valuable, it all depends upon : Author... Illustrator ... Condition ... Scarcity ... Demand. This could be an academic piece, ie one which will have interest to academics.
I certainly hope that yours turn out to be an attic find and are valuable, but maybe be prepared to be disappointed. I have some lovely old books, in immaculate condition, and which are fairly uncommon, but which are worth very little.
Good luck, and don't give up!