50 bucks? Come on, you can do that yourself, really

At least, depending on what you want, you can easily just cut the battery 'holders' and throw the battery to hell. This, of course, means adding a similar battery will be harder, but you don't want to do that anyway.
From the tons of posts about battery leakage, it appears that what people mostly do is wire a couple of wires to the battery terminals and then attach the new battery somewhere away from the motherboard.
Me, I just soldered the old one off, and resorted to using a timeserver

BTW: I am assuming it's the barrel-type battery that I had - were there any others for the a4k? And also I don't know anything about amiga repairs, but removing the battery without reattaching a new one won't damage anything (on the a4k, at least).
Sincerely,
-Kenneth Straarup.