"Reduction" as an alternative means using fewer animals. Reduction is based heavily on the validity of statistical inference. It is also based on efficient use of animals, that is, using the same animals as much as possible up to but NOT including multiple major surgeries.
Finances should not dictate the numbers used; the only valid criteria for determining numbers of animals to use are statistical. A researcher must plan to use the minimum number of animals required to produce statistically significant results. Too few animals will require replication of the procedures and ultimately result in using more animals. Allowances should be made for attrition and poorly collected data in planning numbers.