2 stepper driver like M542 = $ 100
power supply 24V = $50
now comes the tricky part, you can use the AW608 DSP from light object they upgrade them with wistle and bells all the time and it needs tweeking and relearne = $ 500
or you can use the DF211 from thunderlaser what is easier but dont get much wistle and bell upgrades is after my experience a lot of easier if you realy wana do work and not a lot of experiments = $ 450 to $ 500.
if you wana do a real upgrade depending on what kind of laser power supply you have if you have a PWM power supply allready you dont need one but if you only have the analog then you should consider a PWM supply = $ 250
the DF 211 you can get from Thunderlaser - Laser cutters, laser engravers, laser engraver, laser, cutter, engraver, CO2 laser ask for ken, they are in china but very good
or from light object what is Lightobject.com Sacramento (Elk Grove) DSP CO2 laser machine & Parts. Solar panel & Electronics Supplier all of Northern California then talk to marco they are in the US and very helpfull.