Driveshaft repair recovery questions

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I have a couple of questions about driveshaft repair and sorting out how far I will need to go to get my driveshaft straightened out. Recently, I took my car to a shop, recommended by a friend, to have new flex plates and center carrier bearing installed, due to a slight droning noise from the center console. Well, a long story short, it was a disaster! Returned after a drive of only a couple of miles and limped back with flashers at a top speed of 10mph. Failure was blamed on the universal joint. The rear shaft was replaced with a salvage unit that was supposedly balanced. After 5 days in the shop, I picked it up a second time. After a drive of about a hundred miles, there is now a major vibration at 30-40mph but smooths out some after that. There is still a droning noise.

I've got the car jacked up and did an initial inspection, with the driveshaft still installed in the car. From what I've read here in a couple of DIY posts, it appears the front flex disc is installed incorrectly. Correct me if I'm wrong but isn't the raised ferrule, of the flex disc, supposed to fit in the flange of the driveshaft?and the raised ferrule into the flange on the rear of the transmission shaft? I believe it is currently backwards due to a "wave" in the edge of the disc. The disc doesn't appear to be shredded but I've bought new ones out of fear that their integrity may be compromised by this.

Also, don't the shafts need to be balanced as an entire assembly? From what I've read in the Haynes manual, the purpose of marking the shafts before disassembly is to keep the front and rear portions splined to the original balance positions. How can only the rear portion be balanced?

If I have to remove the entire shaft and have it balanced, as a matched set, how much am I looking at cost-wise? This whole scenario just disgusts me at the moment. (I don't blame my friend, he has been a prince with driving me back and forth to the shop.) I've resorted to trying to salvage this repair by doing the work myself, on a gravel driveway in the cold. Please, a little encouragement is needed.