The main difference between our numbers is that I set the ROI for the glowforge at 6 months, which means it pays for itself twice per year. $4k is considerable money but in a business context it is not worth carrying the debt and interest for a year or more. It’s a relatively small amount in context and can be paid off way sooner so actual return can be realized.
The hard part is keeping the laser busy, especially in the start-up stage because most of the time is going to be spent acquiring customers or doing design. There will be only so much time left for business, especially sharing it with a regular job and family. Let’s cut your 500 hours in half to 250, which averages out to 5 hours per week of billable machine time. That still might be tough to achieve but if you do, that fulfills the goal of 2X ROI and puts you into a good position.
For reference, there are industrial laser shops charging $120-$200/hr for machine time on units that literally blow right through stuff in a flash.
If you want a more relatable reference, Ponoko.com has instant online quotes for laser cutting for makers. Last time I poked around there was ages ago and their rates were around the same $45-60/hr mark.
Universal and the other big laser guys recommend $1-$2/minute I believe.
No reason to leave good money on the table and trying to compete with the unwitting hobbyists and knock-offs on Etsy!