The New England Patriots star quarterback is holding a private signing session at the end of the month -- and TMZ Sports got a hold of the pricing sheet.

It ain't cheap ... but it could be a GREAT investment.

We started tracking Tom's autograph prices back in Feb. 2017 -- when it cost $850 for a signed photo.

Fast forward to now ... that same photo will cost $1,049.

A Patriots mini-helmet in 2017 was $900 ... now, it will run you $1,079.

There's a deal on jerseys -- in 2017, Tom would sign your uni for $1,200. Now, he'll do it for $1,099.

And, if you're an artist who's created an original Tom Brady painting, TB12 will sign it for $2,199!

The session is being held by New England Picture by way of Tri-Star -- which has held several Brady signings in the past.

One of the interesting notes ... the public is NOT allowed to attend the signing. Meaning you have to submit your items beforehand and you'll get 'em back after the event is over.

So, yeah ... the prices might seem steep -- but the way they've been appreciating in value, might be a great deal!