Just wanted to report that I used a GoodRX coupon at Costco this morning to fill a prescription for daily tadalafil, 5mg, 90 tablets, and the cost was $33.34. The coupon had said $33.33, which is pretty close. :-) The tablets were manufactured by Burel Pharma.
Another cheap source, which I have not tried, is PharmStore.com, a “Canadian” pharmacy with free shipping to the US. Their cost is about $35 for 90 tablets, plus 5% if you use a credit card. Prescription required, and 2-4 weeks shipping time.
So it looks like GoodRX/Costco is the best source in the U.S. This is still about twice the cost of a liquid, but buying a legit liquid has always been problematical, and it seems a number of the traditional research liquids sites have shut down. So at about 37 cents per day, these cheap tablets are a pretty good option.