Is there a way to connect a traditional PS2 keyboard to my laptop
using Bluetooth? I imagine I would need some sort of PS2-to-bluetooth
adaptor that I would plug into the keyboard, which would then relay to
the laptop's built-in-Bluetooth. Thanks.

I believe I can say that no such device is likely to exist, due to
power requirements. Because a PS2 keyboard receives all it's power
from the host PC, it would not have any power to supply to the
adapter. So while it is possible that there is some kind of adapter,
it would have to come with it's own power source, likely batteries. As
such, the cost would end up being close to a standard bluetooth
keyboard anyway.
The bluetooth specifications calls from power consumption between
0.3mA and 30mA, tremendously low, but still requiring some kind of
power source.
Here's some information on the bluetooth specification:
http://www.ece.virginia.edu/~mmz4s/papers/ECE613project_bluetooth.pdf

I was going to list Bluetooth keyboards, but they do seem to still be
rather expensive, unfortunately.

I hope you find something that suites your purposes.