It can be difficult to find a good replacement laptop battery for a decent price. It seems you always need one at the worse time and have to pay a premium if you want to go to a brink and mortar store. They charge you more mainly because they can, then they also have to cover their overhead, which is not cheap.
Recently I was looking for a replacement battery for my old Dell but was not in any hurry to get it, allowing me to be ok with waiting for shipping. Actually I did the math and I could have it overnighted for cheaper than the store by me, which is sad. It was simple all I did was Google Dell Laptop Batteries and found a great site that had even the hardest batteries to find including the Dell Inspiron 1525 battery and Dell Inspiron 1545 battery which I had a hard time finding when I was looking for them for work.
On a side note, one thing that is quickly becoming a problem when it comes to replacing laptop batteries is Ultra book. I love the lightweight design, battery life, and power for the size they have but the battery is internal making them hard to change. Some companies will void warranties if you change the battery yourself so just be sure to check.