I use a 2000ml Erlenmeyer flask to make a about a half gallon starter and pitch my original White Labs tube. When that has fermented out I sanitize six or seven 12 oz bottles and caps. Then I swirl the starter until all the yeast is in suspension, and use a lighter to flame the neck of the flask for sanitation. Using a sanitized funnel I pour the original starter into the bottles and cap them. I keep the bottles in the fridge and then make a starter as normal prior to brewing. I have read that this saved yeast should last 6 months or more in the fridge.
The benefit to this (other than the cost savings) is that it is presumibly more sanitary than repitching several times onto the yeast cake. I have used this technique on about a dozen different batches with outstanding results. As a quality control I even used a fresh WLP001 vial with a starter, and then one of my saved bottles of WLP001 with a starter in a split 10 gallon batch and there was no difference at all in taste between the two.
Here is a better explanation