It's very easy to build your own with a ton of actions out there.
You'll have to pick your cartridge first though, as that will dictate if you need a short action or long action receiver.
Remage and Savage barrel nut options are out there, but most people prefer shouldered pre-fit barrels for greater accuracy potential and more solid lock up to the action.
Short action will be a bit cheaper and have more options for stocks/chassis, Magazines, etc.
If you pick a popular action (Zermatt/Big Horn Arms, for example), a bunch of barrel makers sell pre-chambered shouldered "Pre-Fit" barrels (like the Remage, but no barrel nut) so installing them, replacing them, etc. is super easy. You just need a barrel vise and action wrench. Just vise up the barrel, screw on the action and torque down with the action wrench. With barrel nut options, you also need go/no-go gauges to set chamber depth and check.
Being able to replace the barrel easily can be more important that you might think too. A lot of these cartridges can be barrel burners.
For actions, I like Zermatt and American Rifle Co. (ARC) due to the controlled round feed options. American Rifle also has some neat and innovative technology, but it's not as popular, so not as many off-the-shelf shouldered barrel options (they do take Savage barrel nut barrels, however. There are a ton of great actions out there now though. All for right around $1K.
Check out the Zermat TL3 and Origin (less expensive option) and the ARC Coup De Grâce. If I were buying today, it'd be the Coup De Grâce, though it does have fewer barrel options (off-the-shelf). The ARC Archimedes has more barrel options (Compatible with Savage small shank barrels like the Origin and such), but not quite as leading edge as the CDG.
Also, ARC makes some great scope mounts and rings. I won't use anything else at this point. Super easy to setup.
You can also get an idea of what other people are using here:
https://precisionrifleblog.com/2024/04/05/best-custom-rifle-action-what-the-pros-use/Keep in mind, this is for PRS "gaming", so it's more targeted to that than just ELR, a lot of shooters are sponsored, manufactures may give more product away for "free" to shooters for visibility, prizes, etc.
However, you'll see a good list of the actions, chassis, etc. that are out there.
Lots of other articles on that site as well about cartridges, pre-fit barrels, etc.
Chris