paperwork for self negotiated sale

[Lin-Chuan Lee]

I was starting process to sell a rental building and notified tenants as a courtesy.    One of the tenants then asked to buy property.   If we come to agreement on price, can i get recommendation on how to get paperwork done?    Should I pay realtor a flat fee?   real estate lawyer ?      Property triplex in Portland OR.    Any specific recs for realtors or lawyers would be welcome.    Thx.