Yeah, mending should definitely just be a bill for the corresponding crafting table. It's actually more logical and simpler at the same time 
Mending really should be a part of the core game; it makes no sense whatsoever that you can magic up various hi tech electronic items from a few chunks of steel you mined out of a mountain, but are completely unable to fix a hole in your socks.
Ideally the maximum item health percentage achievable by mending should be dictated by the same skill used for creating the item, so only a master at the craft (barring modifiers like sight and manipulation) can actually bring an item back to 100%. I'd put the 0-skill point somewhere at 40-45% status with a sliding scale up to 100% at 20 skill... or 18, or whatever. That way you wouldn't need a huge skill number to get clothing out of tattered territory, but still require someone actually good at the craft to repair broken items well enough to count as new. If you want to get fancy you could even introduce something similar to medical operation failures where the item actually ends up worse or with a reduced quality level.
I feel some limitation needs to be there to balance out the fact that mending just magically fixes stuff for free except using a colonist's time. Otherwise mending is just too easy to abuse as a cash source from repairing the inevitable mounds of broken raid leftovers.
Mending really should be a part of the core game; it makes no sense whatsoever that you can magic up various hi tech electronic items from a few chunks of steel you mined out of a mountain, but are completely unable to fix a hole in your socks.
Ideally the maximum item health percentage achievable by mending should be dictated by the same skill used for creating the item, so only a master at the craft (barring modifiers like sight and manipulation) can actually bring an item back to 100%. I'd put the 0-skill point somewhere at 40-45% status with a sliding scale up to 100% at 20 skill... or 18, or whatever. That way you wouldn't need a huge skill number to get clothing out of tattered territory, but still require someone actually good at the craft to repair broken items well enough to count as new. If you want to get fancy you could even introduce something similar to medical operation failures where the item actually ends up worse or with a reduced quality level.
I feel some limitation needs to be there to balance out the fact that mending just magically fixes stuff for free except using a colonist's time. Otherwise mending is just too easy to abuse as a cash source from repairing the inevitable mounds of broken raid leftovers.