Help with Cartridge for Pioneer Reference PL-90

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!
when removing the old cart.,lock down the arm and use a small needle nose pliers or tweezers to gently pull off the pins from the cart. When installing a new one i do just the oppisite, leave the stylus guard on and put the wires on and then attach the cart to the headshell. you will need to adjust overhang somehow, the" cheap and good" IMO is the HiFi News test record with alignment protractor included. As far as carts. go, maybe a Grado Platinum ref;Dynavector 10X5; Ortofon OM30; AT 440MLOCC;Denon DL-110/140;Shure V15whatever; or i'm sure there are many other good choices in that price range, maybe someone can elaborate on that.
Thanks for the quick response. What would be the appropriate remedy if I were to break one of the leads? (Since I think they go all the way through the tonearm)
Thanks again
Just be careful when removing cartridge .Take your time be patient and reinstall leads correctly red,white,blue,green.
Michael Percy does sell headshell leads from some companies.
Sometime back in the early 90's my audiophile friends would actually replace the leads with higher quality ones spring loaded.If a lead comes off they can be replaced by carefully soldering a new one in place.But you should have no problems as long as you don't rush things.Purchase a jewlers hat at an electronic store for $5.00 this would come in real handy here.