Must what goes up, come down?

I sure hope so.  I stopped on the way home from Church this evening to fill up the car, using my Kroger discount card to get $0.03 off per gallon.  I gave the guy in the booth a $20 bill, thinking it would be close but would most likely fill up the tank, since the little indicator needle was at about half on the gauge.

It didn't.  I paid $3.559 per gallon with my discount.

I'd quit driving and ride the bus, but that's not feasible.  Where I live, it takes 3 buses to get to any of the three closest grocery stores in town, and the stop is 3 blocks from my house.  Three fares out and back @ $0.75 each = $4.50.  (No such thing as a transfer here; you pay full fare every time you step through the door of the bus).  And let's say I want to go to the Super Wal-Mart here because I need groceries and non-grocery items.  Here's how I'd have to do it:

Blue Line from stop @ Richwood & Charles at 8:05 am, to Depot at 8:55 am
Green Line South from Depot at 9:30 am, to Wal-Mart at 9:45 am
*******shopping, purchasing only what I can carry in two hands*******
Green Line South from Wal-Mart at 11:45 am, to Depot at noon
Blue Line at noon, to Richwood & Charles at 12:05 pm IF THEY HOLD THIS BUS.  IF NOT:
Blue Line at 2:00 pm, to Richwood & Charles at 2:05 pm.  Sure hope I didn't need any frozen food.

Oh, and if they are willing to hold the Blue Line departure at the Depot so I can transfer, it will probably cost me an extra $0.50.

For this to be worth it to me, gas would have to cost 3-4 times what it does now (but then the bus fare would have probably gone up too, right?).

I sort of like these little exercises in practical economics (like the time a few days ago when it looked like Sudafed was going to become prescription-only and I figured out a $15 package of medicine would end up costing me over $100 in actual money and lost income).