A friend in Central America has asked me to buy her a replacement battery for her Sony Vaio laptop.

(the model is VGP-BPS9/B, in case someone already in Tokyo could check)

Is this something I can get a good deal from a shop in Akihabara (or elsewhere in Tokyo)?
Or, am I better off to buy it online from a US store?
The US online price is about $80.

I will be hand delivering the battery, so shipping is not an issue.

thanks for any info!