I do not believe there are any “plug and play” kits other than the pwncnc. I believe that the owner has mentioned the pwnCNC spindles are made by Gpenny. You can find their parts in various places.
If you are comfortable soldering a chinese spindle is not difficult to set up. If you are not comfortable with that level of electrical work, or you dont have a friend who is, save up for the pwncnc.
To install a chinese spindle to your onefinity you will need to:
Source proper shielded 4 wire spindle cable (not difficult)
Source an aircraft connector (one will probably come with your spindle)
Solder the spindle cable to the aircraft connector (fiddly if you are not a good hand at soldering as the connections are quite small)
Check that the spindle has the ground wire connected inside the spindle body; some do not for some weird reason (easily rectified)
Connect the spindle cable to the vfd (actually pretty hard to screw up, just solder on spade connectors or the like and attach them to the terminals)
Connect your power cable to the vfd (similarly to the spindle you will directly connect it to the electronics of the vfd)
Program your spindle (buildbotics has a guide on the parameters you would need, and most are fairly obvious based on the specs of your spindle).
When your spindle is appropriately grounded you will also need to disconnect the magnet from your touch probe and you may or may not need to invert the wiring of the touch probe. You won’t know this until you’re that far along. Its trivially easy but as you no longer need the magnet to ground the spindle you may need to rectify that as well.
It is not an overly complicated process but it can be a dangerous endeavor as you are dealing with a fairly high current device, and trusting the chinese to do things right. If you are not comfortable with soldering or basic electrical wiring I would suggest you find a friend or reach out to someone qualified.
I run a 2.2kw / 3hp huanyang spindle on my cnc. It really poses me no problems and I am quite happy with it. I think most hobby users will be well served by a chinesium spindle as long as they are appropriately safe when setting it up. You can get the huanyang spindle and vfd kit for $375 off amazon. You will need to source appropriate shielded cabling that is made for continuous motion. I purchased mine from “len1007” on ebay. It is $100 now. You will probably want a different water pump as the 2.2kw spindles come with a 220v pump and you probably want a 110 pump. Budget in anywhere from $20 for a throwaway amazon pump to $150 for a recirculator/radiator. If you go air cooled you do not need that obviously. You will need a cable for modbus communication which is i think $25 from pwncnc (you can make your own but the appropriate connector cost almost that much for mine shipped at the time). You can skip that and set speeds on the vfd manually but thats really giving up some of the best benefits of having your machine control the spindle. You’ll need a spare power cable to use for your vfd, anywhere from $25-50 at the big box store of your choice.
A couple nice to haves are a remote cutoff for the vfd. I use a 220v “long ranger” by PSI. If your power outlet is in a more convenient location you may not care. Mine is behind my table.
You’ll want decent quality nuts and collets for your spindle. You don’t need ultra precision for woodwork but an unbalanced nut is loud and who knows, maybe dangerous.
You’re talking about $550-600 before you start figuring new bits, because I know you want some big boy 1/2 inch bits you won’t use that often anyway. They are nice to have though. Flattening slabs with my 3" surfacing bit is a major time saver.
No matter what you do a chinese spindle and vfd is a decidedly more janky option than a very high dollar japanese or german spindle. But, our executional requirements as a practical matter are quite low here, and I for one have never been able to drive a spindle hard enough on a onefinity to even begin to really tax it. So a lot of the differences are essentially down to potential unit life or inability to work at very low rpm, but those low rpm metalworking operations are beyond the primary scope of the 1f in the first place.