A 6 ft tree can absorb a quart of water per day. This cut will also allow improved water absorbtion. Spray the entire tree, including the trunk and undersides of the branches. Allow it to dry before bringing inside. Firm, layered branches.
White fir is good choice.
All of these are generally the most expensive choices. Blue-green needles, layered branches, cost less than firs but more than pines, and are prickly to the touch. Expect to pay slightly more than for a red cedar. Inexpensive, and last about 2 weeks. Any local native tree should be less expensive, and fresher than an import.