Thanks for asking me to weigh in. I have little to add to the foregoing, except to affirm and point out a few things. Excuse the length, please, but there does seem to be some genuine interest in understanding this verse. First, as has been pointed out, the Hebrew word root “shavar” can mean both “break” and “obtain grain.” The two meanings are not related, they are homonyms. (There are many in Hebrew and can lead to rather extravagant folk etymologies).
“Shavar” as “break” has roots in Ugaritic and Akkadian, and parallels in Aramaic. “Shavar” as “obtain (buy) grain” (or “distribute grain”) is of less clear origin, and is not easy to explain if one does not have a background in Aramaic grammar.
(For those that might: “Shavar” is likely a “Shafel” construction rooted in the word “bar”, an uncommon word for “grain”, related to the Aramaic “ ‘ibura”, meaning “grain.” The “shafel” back construction would be “sha’a’ver”, shortened to “shavar” in Hebrew. I can comment on this more at length if anyone is interested).
In any case, I would translate this verse (as literally as possible) as
“Ho! All who are thirsty, go to water and one who has no silver /
go, obtain grain, eat
and go, obtain grain with no silver,
and without price, wine and milk.”
As has been noted, the word root “qanah” means “buy, acquire by exchange or money”, but “shavar” only implies “buy”, but etymologically probably just means “obtain grain” (Just as if I said to someone, “go the market and get some bread”, it implies buy, but not necessarily, especially if I knew that someone is giving it away for free). This seems clear here, because of the words “without silver (money)” are used emphatically.
Beyond the literal translation, what is being said here? First of all, this is Second Isaiah (roughly, Isaiah 40-55), meaning the prophet writing around the time of the Persian king Cyrus (Koresh). Cyrus defeated the Babylonians in around 537 BCE, and the Judeans exiled in Babylon saw redemption back to the land of Israel on the horizon. The dominant theme in Second Isaiah is that God has graciously and lovingly forgiven Israel for the sins that resulted in the Exile in 586 BCE.
The next verse tells us that first one is metaphoric:
“Why do you weight out silver/money for no-bread, and tire yourselves for no-satiety //
indeed, hearken to me and eat well (or “ingest goodness”), and become delighted in the deshen of your souls.”
“Deshen” is word that can be translated as “rich or fatty grain”, but is very often used in the Bible to refer to the spiritual delight of communion with God; see Psalms 36:9. (I find Psalms 36:8-11 utterly beautiful). In essence, they are being asked to take what is graciously, lovingly and freely offered: redemption and salvation. (see the following verses, and Second Isaiah in general).
This poetic meaning can generate a reinterpretation of the words connected to “Shavar”, “obtain grain.” One obscure, but perhaps present meaning of “shavar” is related to this word root’s use in Judges 7:15, “When Gideon heard the recounting of the dream and its “shever”, he bowed down.”
“Shever” can be connected to an interpretation or a teaching, especially one that communicates hope, in that the Hebrew word “sever” means “hope”, spelled just like “shever” in an un-vocalized text.
The Isaiah verse at hand, therefore, is certainly a poetic/metaphoric prophecy offering redemption “at no price”, i.e., in love and grace, and perhaps playfully brings in a nuance of how the word root is used in the Gideon context.
The image of “God’s food” is well portrayed in many places in the Hebrew Bible, e.g., Proverbs 9, where the bread and wine of God are metaphors for wisdom and knowledge of the sacred.
There is much more to say on this, but suffice here to point out that Christian use of these images, i.e., wine and bread related to God’s grace, is unsurprisingly rooted in the Hebrew Bible.