I am interested in an espresso machine in that price range. Any recommendations?
I would prefer a dual boiler

Breville Dual Boiler would be a common answer. A Lelit Elizabeth might be worth a look, too.

I picked up a Lelit Victoria (SB) recently. Aside from some lame metal finishing of the inside stainless edges, I absolutely love it. I'm sure the Elizabeth (DB) would be an excellent machine.

There are quite a few reviews of both on here.

Have never touched one nor had a drop of espresso out of either but Profitec 300 might be worth a look. Quick Mill Silvano, not a double boiler per se but maybe worth a look.

If you're not afraid of a used machine, it opens up a lot of HX and double boiler options in that price range. I don't think you can go wrong with any of the established brands (Profitec/ECM, Quickmill, Rocket, etc.). A double boiler is a little less hassle and requires less of a learning curve than an HX.

You can also get a nice used Olympia Cremina in that range.

It really depends on what you want out of it: ease of use, temperature stability, ability to play around, do light roasts, etc. Do you need to steam milk or just want to do straight shots?

If you don't know what you want, then buy something used. There's a good chance you can turn around and sell it for the same price if you want to try something different.