I have a nice saddle (sette turbo italia) but I have been ridding a lot in a small amount of time while I get back into commuting. To make it worse, I have just been wearing nike dry fit shorts (with liner) and no undies when I ride in. I can tell this is a bad idea due to the soreness I have experienced. I know I need to get some bike shorts to wear under some normal shorts just for padding. I have a few questions :

1. where can I find good pairs that are inexpensive? LBS's really kill me on clothing.
2. how many pairs do you need for a person commuting 3-5 times a week?
3. how do you keep them clean for the commute? Using a Washer all the time seems like overkill..could I do quick washes in the sink at work?

Just sorting it all out.