Suggestions for bookshelf speakers that have great dynamics, budget of $500 used.

The Legacy studios are very good call but again doubt if can be had for $500.
You never know though.

Mapman.
Have no experience of Ohm speakers at all.

https://ohmspeaker.com/outlet-store/

If you can go just a bit more I’d be considering the Ohm Cam 42s here. 

Actually they will sit on 26 inch high solid sand filled stands so can be a decent size in reality.
I guess monitors is a better description that bookshelf speakers.
But active will not work as being driven by a vintage Sanyo receiver, no outputs bar speaker connections.

Are these actually going on a bookshelf? How big can they be?

Vanatoo Transparent One Encore active speakers are the first thing that come to mind. These do it all well and very compact.  You can buy them new on Amazon for $600.   I use a pair in my wife’s sunroom. 

Older pair of Legacy Studio's?

Been doing some reading this morning.
It may take more than $500 to significantly better my existing Silver 3i speakers.
Did not realize this model was still made in England before they switched production to China.

Tbh, there is not much wrong with them but at the very low price I paid I assumed they were a cheaper speaker that it seems they truly are.
Guess I should just trust my ears, the grass is not always greener on the other side!

Still looking at options though.

Lots of options with $500 on the used market. I have not had a chance to hear the Revels. From what I have read I have become interested, however have too many speakers pairs. 

Wharfedale 10.1 or 225 models are pretty decent and much better than their price might suggest. 

I have seen Dynaudio Focus 140s go for around 500. If you have plenty of horses as you say they will be really good for that price. 

Anybody got first hand experience of Revel?
Looking at a pair of M20 CW stands for a fair price.

You might be able to find a dealer willing to discount some B&W 607s. An industry typical 15% discount would bring their price to $595. Saving just a bit longer to step up to these from the typical ~$400 offerings would be a good move IMO. The older 600 series was quite dynamic and some reviews claim the new 607s are as well. 

You could probably audition 20 other brands and not find any more dynamic than Epos or B&W. One exception might be the new Klipsch RP-600M. I haven't heard them yet but many are raving about their dynamics. However, my presumption is their midrange isn't as refined as some of the British brands. 

When you say dynamic and loud, my first thought is Klipsch.  

I sort of figured the Zensor 3 would be more suited to my room tbh.
Silver line is definitely an option, a few on USA audiomart in my price range.
Not heard any paradigm speakers, will research them.

Zensor 3s are nice mellow, have Paradigm 20 v.4 love em! MA Silver also tried, more laid back than Paradigm. Might try again!

I own a pair of Dali Zensor 1s. I purchased them used ($200) from another AGer who wanted to upgrade to the Zensor 3s. The 3s would be better for a 'largish' room, however can't say how they would compare to the Monitors.

A used pair of Paradigm Studio Reference 20s V4 might be just the ticket. I once owned a pair and thought them to be quite dynamic. 

I have a pair of modified Heresy IIs, that might interest you. If you have any interest, you can PM me.....

Have a look at Silverline.  Although perhaps better known for floorstanders, they make some good bookshelfs; you might find a used pair at your price point.

Anybody owned the Dali Zensor speakers?
Both the 1 and 3 look interesting.

Epos K1i currently on sale at Music Direct.

Few other brands are as dynamic. 

I owned and sold a pair of the Spendor S3/5's that fit right in to your budget. They were absolutely wonderful little speakers! However,these definitely aren't rock out at 100db speakers. They did seem to perform pretty well in our 15x25 ft finished basement. YMMV.  The MA's sound like checking out as well.
    Enjoy the hunt!!

With all due respect to the previous poster, the Klipsch have nice and lively sound but a bit bright for my classical music ambitions.

Buying used, you can get a cut above that and end up with even more quality, although for the money, the Klipsch is a nice offering, especially for certain kind of music...

I prefer the MA silver over Klipsch.

With your budget, it would be difficult to out do the MA silver - I love mine with pretty top end sound, and clear mid and tight bass...although lacks refinement of an upper end speakers.

I second the Harbeth previous poster mentioned - they would surely lift you out of a side ways move, and give you an upgrade...but would be hard to find for that money...

Perhaps you can look at Spendor speakers as well...

I've seen some good press on the Klipsch RPM600 and I think they're within your budget. 

Buying used is wise .... I bought for peanuts Mission Cyrus 781 speakers (under 100 bucks) To upgrade that would be buying thousand dollars used speakers (Harbeth probably)... With luck and if you look for you will be the next owner...I cannot say anything bad about them....But they are at the limit of size for budget speakers...They are on my desk between the computer screen on my homemade anti-vibration sandwiches plates...My best to you...