I had never heard of Jason Engle, but he produces some really beautiful work - his isometric maps are gorgeous. If you look at his list of clients, it gives you some idea of the standard of the work (if the work itself didn't speak highly enough already).
In terms of the character line drawings, those are done to a professional standard and unless you are very talented and dedicated (and you would know it if you were) it would probably take years of effort to get to this level.
If you are after high quality illustrations, then you're probably going to have to pay for them. It might be worth cruising around the deviant art pages to look for independent artists who might give you a good price.