I had saved an article from Western Beef Producer on this very subject. For some reason, I can only find the second page of the article.
That page contains a graph on "Cost per pound of protein.
Table 2 shows per-pound price comparison of actual NATURAL protein in supplements (interesting that all the nutritionists I know include only that portion of the NPN that can be utilized by the ruminant. For comparison purposes SUBTRACT the NPN from the natural protein source--anyway we aren't discussing NPN here

) commonly available to many Western beef producers. In this example, 17% crude protein alfalfa hay at a cost of $100/ton was the most economical protein supplement. The 29-cent cost per pound of protein was nine cents cheaper than it's closest competitor. Producers could pay up to $134 per ton for alfalfa hay before the other feeds become price competitive per pound of natural protein.
In it's enterity this was an excellent article. I have kept it for many years and I'm sad that I can't find the rest of it. I will contace WB Producer and see if I can't get the complete article.
We have many customers that have switched from cake to feeding alfalfa hay--not as a complete feed but as a supplement. On grass they feed 5 to 10 lbs. of alfalfa. The cattle also get some dry matter when feeding hay as well.
I appreciate the way Soapweed runs his outfit. In some cases, it just isn't feasible to feed hay when you are set up to feed cake.
One thing I cannot urge enough...get your hay tested :!: :!: :!:
Spending $25 on a hay test can save you thousands of dollars in supplement. In Montana, in 14 years of testing hay, we only found one sample that was too low in protein that it needed something with it. 10% protein hay is good enough for range cows. Just make sure you feed enough of it.