Help with Cartridge for Pioneer Reference PL-90

Hello,
I often read Audiogon for advice and I often find just what I need. I think that this is the first offical thread that Ive started since I can't find much information about what Im looking for anywhere.
I recently picked up an entire Pioneer reference/elite system, which included a PL-90 turntable.
My question concerns changing the cartridge on the PL-90. Ive only been using turntables for about 4 years (Im 24 and they were before my time. I fell into the trap of believing new technology = better and only used CDs until I decided to experiment with vinyl and was hooked). My vinyl collection is growing rapidly as is my collection of vintage tables and various cartridges.
All of the tables I currently own (Marantz 6100, 6200, 6300, and a few Duals) all employ bayonet mount headshells and chaning the cartridges is very simple.
The Pioneer PL-90 does not have a detachable headshell and it appears as if the leads run all the way through the tonearm. I believe that the table still has the stock mounted (which is a fairly low end AT cart). Id of course like to change this, but I am concerned with a couple of things.
First, Im worried about possibly breaking leads when I change the cart and then having to completely rewire the tone arm (which I definately would be too inept to handle at this point). How do you safely change the cart without damaging the leads? Is there a way to remove the headshell or somehow adjust the tonearm to make the change easier?
Also, I have no idea what cart would sound best with the PL-90. Money IS an issue (Im looking for something $300 or less). Im looking for clean WARM sound. The cart definately does not have to be reference quality or top-of-the-line, just something efficient and accurate.
Any help would be greatly appreciated!
Thanks,
Justin