I would recommend that you take care when ordering what seems like the 'right' battery (and the 'right' price) for your specific laptop. While there seems to be a wide and varied choice, I believe that a great many of these batteries available via Amazon, eBay and from online stores will prove to be a waste of money – unreliable, short-lived and some even potentially dangerous.
I have an early 2009 white MacBook and a while ago I was obliged to dispose of its battery because of the swelling issue. I do not use this machine as my main computer. However, my own subsequent efforts to verify a reliable battery source for this laptop have led me to the following conclusions, which may be helpful to you:
1) You could always try to source a 'pre-used' battery for your 2008 MacBook Pro. In theory, you could get one that has enough life in it to work for you for a decent extended period. The trick is to track down a reliable battery of this kind. (I recently bought a previously used battery for £20 (just under 26 dollars) and was assured that it worked, though when it arrived in fact there was insufficient charge in it. I was offered my money back and instead we split the amount I paid. I kept the battery for cosmetic reasons – to fill the gap in the base of the laptop until I get a fully working battery). So, be careful if you go the pre-used route.
2) I have found that for my MacBook there is a UK supplier for the NewerTech NuPower battery, brand-new, as seen on the everymac.com website in the USA. Last time I looked it was priced at around seventy dollars on their site (though the same battery is more expensive from a UK supplier). I imagine a battery for your laptop would be priced similarly.
3) As I'm based in the UK I was also pleased to see that Duracell Direct will supply me with a seemingly reliable third-party battery for my MacBook for about £67 (about 86 dollars). This battery is made by 2-Power and, like the NewerTech NuPower, are the only two seemingly reliable options for my own needs. I suspect this will apply to you too.
There may be perfectly legitimate and decent other third-party batteries out there, but it is something of a lottery whereas the two makes I mention have good reports and, based on their specs, don't seem to be cheap knock-offs as so many are.
It is extremely unlikely that you will be able to source an original Apple battery. Those purporting to be such are unlikely to be what is claimed.
I'm afraid there is probably no easy, cheap answer to your battery needs. I'll be trying the 2-Power due to its price here in the UK and have high hopes of it. Good luck with your efforts.