Going by your laptop model, it appears to take an SATA hard disk. This means that you will need to purchase a 2.5" SATA drive.
What size of hard disk are you after? They come in a range of sizes and the price depends a lot on the capacity. For brand, I have a preference for Western Digital, although any brand of SATA 2.5" should work fine.
The most likely size that came with that laptop is 160GB, so if you're looking to replace this with the same size, this will likely cost around US$50 in the US or â‚¬35 to â‚¬40 in Europe from an online shop. Retail shops tend to charge more, but don't forget to take the delivery charge into account if you order online.