I usually don't like to use meat from the freezer besides chicken breasts, but a market here has some gorgeous standing rib beefroasts at $3 a pound, ridiculous. So I'm wondering, just how bad can thawed rib roasts be (if cooked properly once thawed of course).
I've roasted frozen meat many times without ill effects. Just don't leave it in the freezer for more than 2-3 months. I find this is especially true with fattier cuts, such as rib roast. I used to roast the meat without thawing it completely, giving the outside a nice crispy brown texture and leaving the inside medium rare. Go for it! Enjoy your bargain.
Messaluna is right on the money. But, I would'nt roast it. I would smoke it after thawing out. And I would put a dry rub befor freezing. At that price, I would get as much as I could and save it for a rainy day.
Since most hot smoking is done low and slow (185-200F/ 8-16hrs) to break down the connective tissue of ribs, shoulders or briskets, and since Prime Rib is typically roasted at a high temperature, do you smoke Prime Rib at a high temp, say 325-350F, or do you go with low and slow and pull it once the internal temp hits 140F? Prime Rib around here is not $3/lb and I would hate to ruin a $100 roast.
You wrote: Le't's start by cleaning up a few misconceptions, before getting to the point -- which is a very good one.
"Low and slow" is a colloquial term without a universally definition; but it's almost always hotter than 210F. Cooking at temperatures below the boiling point of water is another thing altogether. It's also not particularly safe, and I can't recommend it.
Cooking BB ribs low and slow typically takes about 4 hours, and spares take about 6.
Most charcoal and wood-fired smokers have a relatively restricted range of temperatures which they can hold steadily. Usually the range is within a few degrees of one or both sides of the 215 - 235F range. It's the rare smoker that can hold a steady 325F.
You can smoke a standing or prime rib to 140F internal at a low and slow 225 - 250F, and do a pretty good job. However, since the roast won't absorb much smoke after a couple of hours, you might just as well transfer it to the kitchen oven and finish it at a higher temperature for a quicker cook and a better crust (aka bark).
If you're interested in more specificity, let me know what kind of smoker you have, your experience level with it, and anything else you think might be relevant, and we can start getting specific.