The Texas A&M University at College Station offers Ph.D in Interdisciplinary Engineering via Online. URL: https://engineering.tamu.edu/mtde/academics/degrees/graduate/phd-itde/online-phd-itde.html
I couldn't find the fees - don't like that, Famous schools or not. I DID notice however that the school has slapped a supplemental charge on top of normal tuition for all Distance course ranging from $40 to $540! a credit-or maybe it was per course, I couldn't find it to re-check. Don't like that either. I figure the cost will be Texas-sized i.e humongous. I spent 1/2 hr went thru entire sitemap - No dollars-and-cents tuition fees! What is this - a game? Maybe Texans have so much money they don't care or need to know....
Best I can get - from another source - is that grad. tuition at Texas A&M starts at $22,196 for out-of-state students. Figure in an online additional charge and a supplemental on all engineering grad courses, that is built into tuition. The PhD is 64 units beyond a masters. You engineers will have to figure how much the supplements are and how long it takes to complete 64 units, including dissertation etc. I'm guessing if you do this in 3 years it's probably $100K - $110K all told. Maybe it takes longer, I don't know. Thanks to Texas A&M being reticent about posting fees and supplemental costs, I doubt this estimate of mine is a very reliable figure. If the professors are HALF as hard to get info from -- it will be a very challenging program indeed! Note: there were pages on GIVING all over the place. No mention of fees could I find.