Isn’t "higher-priced products" with an adjective ungrammatical for the correct "more highly priced products" with an adverb?

Question

The phrase higher-priced products is very common, but isn’t it grammatically incorrect?

The adjective higher is being forced to servce as an adverb here, so the phrase should instead be more highly priced.

What’s the verdict?

Answer 1

Both are correct with long-established usage. You can say "more highly" if you like, but according to dictionary.com:

adverb, high·er, high·est.

• at or to a high point, place, or level.
• in or to a high rank or estimate: He aims high in his political ambitions.

American Heritage Dictionary agrees:

adv. higher, highest

1. At, in, or to a lofty position, level, or degree: saw a plane flying high in the sky; prices that had gone too high.
2. In an extravagant or luxurious way: made a fortune and lived high.

See also:

• Highly etymology
• High etymology

Answer 2

Aiming high, jumping higher, and climbing highest

A word does not have to end in -ly to be an adverb, you know. Examplars include soon, thus, early, late, often, always, low, high, fast, slow, deep, more, well, not to mention sooner, better, less, earliest, slower, most, highest, later, least, worse, best, worst, deeper, fastest and all the many, many others just like all of those.

I’m afraid that this is a case of what we call hypercorrection, which per the Wikipedia link given means:

non-standard use of language that results from the over-application of a perceived rule of language-usage prescription.

That’s because the word high is now — and ever has been — a super-common and perfectly fine adverb in the English language.

Documentation

The OED entry for the adverb high details no fewer than 77 different senses (comprising 19 main senses and 58 subentry senses) along with 466 citations, many dating from Old English itself more than a millennium ago, and with many stretching all the way into our current decade as I write this.

Here are just a scant few of those 77 senses:

1. a. To or into a high place, position, or point; so as to be high or tall.

   b. In a high position; at a high altitude; far up, aloft.

   c. Esp. with reference to the movement or gait of a horse: with the feet lifted relatively high above the ground. Cf. low adv. 1c.

   d. Far up towards the source (of a river).

2. In or into a high latitude on the earth's surface; far from the equator.

3. c. figurative. Towards or at a lofty or ambitious goal. Frequently in to aim high (cf. to aim high at aim v. 5a(b)).

4. c. At a high rate, amount, or price.

   d. Richly, luxuriously; to excess. Now chiefly in to live high; cf. to live high on the hog at hog n.1

5. With reference to music or song: at a high pitch; in or to a high note or range of notes.

That doesn’t even count the many senses for the comparative adverb higher and the superlative adverb highest. Those too have been part of English since Old English, back when the years were numbered using three digits alone. Here, though, are a few of the many splendid citations more recent than the Norman Conquest provided there, with the word in question here rendered in boldface which the OED uses an underline for:

• 1913 J. Muir Story my Boyhood i. 18
  We tried to see who could climb highest on the crumbling peaks and crags.
• 1961 F. C. Avis Sportsman's Gloss. 111/2
  Beamer, a ball aimed high by the bowler, often to the height of the batsman's head.
• 1972 D. McCulloch Great Bridge xxi. 474
  It would be ‘her remarkable talent as a peacemaker’..that he would praise highest.
• a1979 N. Ray I was Interrupted (1993) 100
  Lines went haywire, actions went haywire, Arthur got thrown higher than a kite.
• 1992 Independent 4 Aug. 12/3
  What are the implications of this for women aiming high? Must they be better, more hard-working than the men? Must they play office politics?
• 1998 A. Taylor Suffocating Night (2003) ix. 64
  Howard waited and watched as the sun climbed higher in the sky.
• 2008 N.Y. Times (National ed.) 7 Oct. f11/5
  Typically, break fees are about 3 percent of the deal value, but they are creeping higher.
• 2010 E. Verhagen in D. J. Caina et al. Epidemiol. Injury in Olympic Sports xxiii. 330/1
  Biomechanical studies have revealed an increased incidence in jumper's knee among those athletes who jump highest.
• 2011 R. Clements Revenger vii. 47
  It was drawn by four white stallions, all proudly harnessed with feathers and shields, their forelegs trotting high and in time.

Those are all perfectly fine adverbs, as I’m sure you’ll agree.

Summary

Therefore, returning to your original example with all this in mind, when one product has been given a higher price because it has been priced higher than another one is, then that first product is certainly the higher-priced product of the two.