I work in Texas, helping people design, build, stock and manage lakes and ponds. Here's solid advice. Bring someone on site who knows local soils. Find a nearby earthmover, or several, and talk with them. Talk with the closest NRCS district conservationist, and look at soil maps with them. If you get solid, positive information, and your experts are confident your soils have a chance, dig test holes, and look at what lies underground.
If all parties concede and suggest a liner, look in Pond Boss, and call Colorado Lining Company for an estimate.
One point that leapt from your post. My dear friend Mike Otto, lake builder extraordinare, once grabbed me by the collar after a seminar, and while choking me, make a valid point. I had been telling attendees to "find non-porous soils to build a lake". Otto, in his inimitable way, pointed out to me that, "there are no such thing as 'nonporous' soils." He said, "If soils weren't porous, there'd be permanent puddles all over the place." He's right. All soil leaks, so when building a dam, a good earthmoving contractor processes and mixes available soils to create a barrier, to minimize leakage.
So, bottom line is this...check your soils. They will tell you whether or not you need a liner.

Teach a man to grow fish...
He can teach to catch fish...