While dedicated studio lights are much more powerful, speedlights are far more portable and can be a perfectly viable substitute in a lot of situations, especially location work where full monolights would be cumbersome and tedious to use. This great video will show you how you can use simple speedlights and portable modifiers to shoot professional headshots anywhere you go.
Coming to you from Tim Kelly's Master Photo Techniques, this excellent video will show you how you can shoot headshots using nothing but speedlights and small modifiers — in this case, a set of Godox V1 flashes, though you can use a variety of speedlights. Monolights are certainly great and enable the usage of other modifiers, but often, speedlilghts have plenty of power for things like headshots, which can allow you to create a very affordable and portable kit. As Kelly mentions, you might have to bump your ISO slightly in some scenarios, but do not be afraid to use an ISO like 200 or 400 if you need it. Check out the video above for the full rundown from Kelly.
And if you want to keep learning about lighting, be sure to check out "Illuminating The Face: Lighting for Headshots and Portraits With Peter Hurley," which is currently on sale along with the rest of the Fstoppers store!