Offer to babysit your sisters younger kids for the cost of feeding them
Give them a crash course on trimming, and tell them if they do it right they will get an Xbox.
Feed them redbull and pizza.
Leave them be for 5-27 hours, depending on yield size.
Send them back home to Mom with no Xbox.
total cost for food and drinks = $0
Having
slave... I mean "free" labor, direct from your own trusted nieces and nephews = priceless.
It also helps being the "scary Marine Uncle"... to get them motivated and shit.