I have been researching the exact same situation RF45 CNC conversion vs used VMC. Years ago I swore I would never go down the RF45 CNC path again, my old one never worked as advertised and I ended up scrapping it after over $10k invested and much frustration.

Today though Charter Oak offers a RF45 variant mill with some features that has me re-thinking that decision. 3hp VFD option coupled with a quieter belt drive = 5,300 rpm spindle, that's a plus my old RF45 2,000 rpm spindle was painfully slow. They have increased Y to 12" for a 12x26 inch work area. They replace the bearings and are good for 7,000 rpms. They tell me they have solved the issue of crap ways with loose and tight spots. They also have a newly designed CNC kit for them, direct drive (no belts) servo's with integrated encoders and drives. I very nearly plunked down the cash for one of these last week but they were all out attending a show in PA. That slowed me down and I started working my calculator...now I'm on the fence again.

Mill $2,350
CNC Kit $6800
3hp VFD option $850
Belt drive $785
Shipping $540
CNC computer $600
Stand $700
Enclosure $1,000
Flood coolant $300

So $14,000 and for another $6000 I could just buy a used Haas and get way more machine with a tool changer and chip auger. The problem as some mentioned is what if the used Haas needs a bunch of repairs right so I checked into this recently and the components cost less than I expected. More research is needed. VMC power requirements eliminate most of the Haas mills for me but the Haas mini mill 2 can run on single phase 40 amp that's doable. The 20x16 work area is a bit smaller than I would like but for a garage shop that's not bad. 6,000 rpm spindle. 600 in/min rapids, 500 in/min feeds. Rigid tapping. Programmable coolant nozzle. LM ways. For only $6k more than a RF45 conversion? The only reason I hesitate is the potential for an expensive repair on the used Haas.