I have just bought a remington 870 express magnum with the 20 inch fully rifled barrel and would like to know if there is any kits to make the trigger pull lighter.  I have seen on ebay that they sell a spring for about $10.  Is this all i need?  This will only be used for hunting deer in NJ so i can't go crazy with the mods.  Any help or input will help.  THANKS

The Express already has a fairly light spring for a shotgun.

What you can do:
Clean the trigger group out and re-lube with a good lube like CLP Breakfree.
Then use a good gun grease to grease the contact surfaces of the hammer and sear, and the sliding contact areas where the trigger extension rubs against the action bar lock on the left side of the trigger group.

Then assemble the group back in the gun and dry fire 100 times.  This will also help smooth up the action.

Next, if it still isn't light enough,  you could replace the trigger/sear spring.  That's the coil spring that goes from the trigger to the sear.
Unfortunately, I don't know of any aftermarket lighter weight spring to replace it with.