I need some advice about upgrading my fork
OEM Suntour forks are awfully terrible. Almost any other after-the-market fork would be better.
I would recommend going with an air fork as the technology is very much polished now, so there is no need for coil. In the price range that you have designated, there are many decent forks, however not so many vendors to choose from, and one is clearly dominating.
I would focus on getting a compatible fork in the first place; that is, all the parameters:

wheel size (26/27.5/29),

travel (100-180mm),

steering tube type (straight/tapered),

axle system (QR/through-axle)

axle length (&quot;normal&quot;/boost)

brake mounting system (disk ISO/post mount or rim V-brake)
— must match. Let's not forget about the color, although it is mostly black.



Can I get something with remote lock for this price range?

Not sure about that. However, I've never found a need for a lockout, be it on the fork or a remote one,  — a good fork should just work, and the lockout only takes space on the handlebars.

What features should I look to make a long-lasting investment?

You need to service your new fork periodically. I've seen vendor's recommendations to do it once every 50 hours of operation. For my taste, that is way too often. Once a season should be the lowest frequency for the service.