Help with Wireless, Airport, Repeater

[B Gardner]

I would like to throw this out to everyone hoping I can get some help.

Here is my setup:

Basement office in a single story ranch type home.
Airport Extreme Base Station is located in basement. Connected to the 
LAN port of the Airport is a NetGear 8 port router.
A DSL modem is connected to the WAN port on the AP base station. Other 
computers downstairs connected to 8 port router.
AL PowerBook has AP Extreme. When working on PB in basement office, I 
connect it to the ethernet cable, which is connected to the 8 port 
router mentioned above.

Problem:
At times, I need to use the PowerBook upstairs on wireless through the 
AP base station but when I do, the signal is weak and unusable.

To help, I connected a 6dbi omnidirectional external antenna to the 
Base Station. Helpful but still weak and at times drops signal.

Questions:

Is there a way to set up a "repeater" (or would it be a "bridge") 
upstairs to extend a signal from the airport and make the reception 
better upstairs?
What third party wireless equipment could be used in this instance?
I know the Airport Express will be useful in this case, but is there a 
suitable third party source that will work and is less than 120.00?
(For example, I have seen Belkin bridges as well as Buffalo makes a 
repeater. What works with a Mac and Airport?)

I am hoping someone out there has done this and has already figured 
this out.

Thanks for reading.

Byron