I have set all prices to 0 and then 

"OwnerOnly": true,
"UseCurrency": false,
"UseEconomics": false,
"UseServerRewards": false

still says in chat i do not have enough 

will take a look at this for you

this is me trying to buy one in chat with command 

/tree oak

Getting the same. Adjusted all perimeters to 0 and it still will not purchase. Added a crap ton more Scrap just in case, still get the same message as above. "You Do Not Have Enough For That"

i dont have any currency plugins on my server but regardless here is what i set to get them for free

"OwnerOnly": true,
"UseCurrency": true,
"UseEconomics": true,
"UseServerRewards": true