Best cartridge under $450? No Grados please

I'd second the Denon DL-103D. I think it's one of the
great bargains in high end audio. It's available through
Denon USA for about $320. Search this forum or the Vinyl
Forum on audioasylum.com and you can find the phone number
for them. I'm using a Lehmann Black Cube SE phono preamp
which works nicely. Because the 103D only outputs about
.23-.25 mv it does require a higher gain phono preamp.

I saw on Ebay Dynavector 20X for $350 new. I think, the same man sells here too.But it was low output MC ;perhaps, he has high output as well,if you need one. What is your current set-up ?

There is no such thing as "best".

From my personal experience I would recommend the Goldring G1042 MM cartridge. It has a 6.5mV output & it really sounds excellent. Your present phono stage should work just fine with the G1042.
Here's their website:-
http://www.goldring.co.uk/

They also offer various MC cartridges such as the Eroica H (2.5mV output), which is also supposed to be a good buy.
FWIW. IMHO.

I ran the Shure on my Rega P3 (which I'm guessing is what you have)for two years and replaced it with the Dyna about two months ago. You can click on my system link to see what kind of gear I'm using, and it will be clear that my priorities are not neutrality or transparancy, but rather a rich, smooth, enjoyable presentation. In fact, my system isn't really resolving enough to highlight dramatic differences between cables and such. Not surprisingly then, I didn't find huge differences between the two, though I ended up staying with the Dyna. Here's my assessment, then:

The Dyna's bass seems a bit flabby in comparison to the Shure. The Dyna has a richer midrange and more "sparkely" highs. Both are very quiet, with maybe a slight edge to the Dyna. The Shure is a better tracker, though the Dyna is no slouch in this area. The stylus of the Shure seemed to attract gunk more readily than does the Dyna. The Dyna seemed more sensitive to VTA than the Shure. The Shure has a user-replacable stylus and is easier to mount to the arm. The Dyna is better looking.

In summary, I found the Shure to be more lean/transparent, while the Dyna seem more lively. I liked them both and could have easily lived with the Shure for a couple more years.

Like so many things, I suppose, the right choice depends on what you're looking for. Good luck and have fun.