Marx seems to be making an argument in line with the so-called 'single system' approach in pages 423-434, where he criticizes Proudhon's explanation of overproduction. Proudhon understands overproduction to occur because capitalist adds interest and profit to the real value of product, i.e. its price is an overcharge on top of its real value, and as a consequence 'the worker cannot buy back his product.'
Marx counter-argues that capitalists' profit does not come from overcharging, and that surplus-value is already included in the value of the product.
There he makes several interesting statements:
"It might be said that necessary labour time (i.e. the wage) ... is .. determined by the prices of [subsistence goods] which already include profit." (p. 424)
"It is clear ... that the wage paid by the [capitalist] to his workmen must be high enough to buy the necessary [subsistence good], regardless of what profit for the capitalist may be included in its price." (425)
These seem to be consistent with the way the value of variable capital is determined not by the value of wage goods but by wage within the New Interpretation by Foley, etc.
Marx makes comments: "The puzzle arises simply because (1) price and value are being mixed up; (2) relations are brought in which are irrelevant to the determination of value of such." (425)
The first part is obvious from the above citations. 'Relations' referred in the second part seem to imply those which make price deviates from value, such as competition, 'fraud, reciprocal chicanery,' etc.
In sum, in these pages I read the single-system argument of Marx's as follows (citing without notice):
1) The determination of prices is founded on the determination of values.
2) But new elements enter in, and the price, not merely being the value expressed in money, but becomes further determined as itself a specific magnitude.
3) "Necessary labour time" i.e. the value of variable capital is determined by the prices of wage goods.