I think its important to note that whilst Karl Marx was a critic of capitalism, he was not a utopian in the way that some anti-capitalist thinkers have been; i.e to my knowledge he did not try to remove himself completely from capitalist society.

Capital was published by a normal publisher and sold like any other book. I do not know about the pricing of the book but I have not seen anything that would suggest its distribution and pricing were in any way calibrated by anything other than commercial concerns. "Getting it out there" was not as much of a problem as you'd think, given that by the time the first volume of Capital was published, Marx was already relatively well known as a writer. That being said it was hardly a bestseller; it sold best in Russia, but in germany it took several years to top 1,000 copies.

Marx himself had been editor of political journals like the Deutsch–Französische Jahrbücher which, again, whilst not run for the purpose of making money, were not, to my knowledge, sold at an artificially low price or given away to workers etc.

The problem with doing such things would be - who would pay for it? Engels already had to spend a fair amount of money helping Marx. Even working commercially, the journals Marx edited often ran into financial difficulties, partly because their work was usually suppressed and banned in his native Prussia.

I'm not sure he would have had misgivings - Marx was not beyond participating in the capitalist system when he wanted to. He rather famously dabbled in trading stocks when he thought he could make money from it:

I have, which will surprise you not a little, been speculating — partly in American funds, but more especially in English stocks, which are springing up like mushrooms this year (in furtherance of every imaginable and unimaginable joint stock enterprise), are forced up to quite an unreasonable level and then, for the most part, collapse. In this way, I have made over £400 and, now that the complexity of the political situation affords greater scope, I shall begin all over again. It’s a type of operation that makes demands on one’s time, and it’s worth while running some risk in order to relieve the enemy of his money.

(This is the best source I can find by googling. Also who knew that google allowed you to look at the Collected Works of Marx and Engels?)

Given that, I don't think that Marx would have had qualms using commercial publisher to get his work published. Though I don't doubt he probably had some testy words about them with regards to his always being under pressure to meet deadlines!