I am an MC fan as well. I would not recommend the grado offerings, except that you can replace the stylus. However, I have experience with replacing the arm/stylus of a Benz micro mc (two of them) thru a vendor in New York. He does a great job. $300-400. Yes, the sound is slightly different, but excellent nonetheless. Feel free to email me to get the info.
Your Dynavector is better than the recommended grado, particularly with a new rebuild. Have you tried the Dynavector 10x5, mc high output? It's very good with rock. In your price range.
Finally, 2juki (Hong Kong) on eBay offers great deals on cartridges and accepts returns if the cartridge arrives damaged. He's been dealing in high end cartridges for 20 years, at least. Very credible. I have bought two cartridges (10x5 & Audio Technica ART9). FWIW, the ART9 is excellent but the same price a the dv20x
Goodluck