Which route for 2nd pc?

After a few upgrades I have a spare 2060, 2x8gb ram and a psu. I’m wanting to build a second pc for my son. My rig is using a 3060ti and an r5 3600 on a b450. Question is do I upgrade my mobo and cpu (b550/5600x probably) and put the b450 and r5 in the new build or keep it as is and get a more economical board and cpu for the new build? I’m still fully happy with the r5 3600 in my machine but would trying to save a buck here be a mistake? Cheers for any input