Chainsaws are great for cutting beams. One style of beam cutter is basically a chainsaw attachment for a circular saw https://smile.amazon.com/Prazi-USA-Blades-Cutter-Drive/dp/B0000224SA?sa-no-redirect=1
$139 on Amazon supply your own circular saw. Pick up a used worm drive is my suggestion.
Not bad for $140 if you have the Skilsaw already: https://www.amazon.com/Prazi-USA-Blades-Cutter-Drive/dp/B0000224SA/ref=mp_s_a_1_4?dchild=1&keywords=prazi+beam+cutter+12&qid=1610413043&sprefix=prazi+beam+&sr=8-4
Nice! Pretty piece of wood!
Next time buy one of these though. You'll never regret it!
http://www.makita.ca/actionimages/5402NA_act_1.jpg
(Ha, just kidding...although it would be great to show off)
Here is another option:
https://www.amazon.com/Prazi-USA-PR7000-Cutter-4-Inch/dp/B0000224SA
Ok, done now...