Welcome to LantusLand!
There are number of options, so your best bet is to call around to your local pharmacies to see how much they charge. I found pretty wide price ranges, and finally settled on the local Target pharmacy. In the long run, the Solostar pens are the most cost effective approach, but they cost more up front - although some pharmacies (like my local Target) will sell the pens individually (this is how I buy my Lantus. One pen costs me $45, and it lasts almost 2 months). When we buy the pens, we use them the same way as the vial, using a syringe to draw the insulin from the pen; you don't use the needles that normally come with the pen.
Likewise, I also found that my local Target had the best price on the Lantus vial.
The "expiration date" on an open vial or pen is 28 days from initial use. However, when treated carefully (stored in the fridge, not shaken or rolled, no air or Lantus injected back in), it can last considerably longer than that. Some people here get as much as 3 or 4 months out of a vial before it starts petering out.
Again, welcome, and feel free to ask any questions you need answered!
Amy