Why universal background checks are unconstitutional

So the latest 'common sense' gun control policy being debated is universal background checks.  What's that?  Well, currently when you go to a gun shop you need to get a background check, but in some states it's legal to buy guns privately.  Most states limit personal sales to rifles only.  A 'universal background check' law would require private sale gun buyers to get a background check.

Let me explain in more detail how gun sales work.  The gun shop purchase is simple... walk in, pick out a gun, get the background check (which is an extra fee), buy gun.  When you buy a gun online it needs to be shipped to your local gun shop (contrary to the uninformed gun control advocates out there).  Once it's at your local gun shop, you need to pay for the background check, pay a extra 'transfer fee', get your gun.  The extra 'transfer fee' is also paid when two people go to a gun shop to change ownership of a gun, i.e. selling hand guns in states that require background checks even on personal sales.   In both cases you're paying for the background check, and a transfer fee.

The transfer fee is for using the gun shop owners time and resources since they won't make any money on a gun sale.  For the background check fee, it depends on the state where that fee goes.  The ATF and fed govt don't charge for the NICS system (the system used for instant background checks), but a lot of states do.  In the states that do, the FFL (gun dealer) calls the state NICS hotline to do the check, and at the end of the call they get charged a fee, and that fee is passed onto the buyer.  This current system can pass constitutional muster because you're not forced to buy a gun from a gun shop if you want a gun, there are private sales.

So now the unconstitutional part... A universal background law would require citizens to pay for access to their constitutional right to own a gun (remember poll taxes?) by adding a fee to private sales.  The left will argue, "if the right can force voter IDs, then we can do background checks".  The problem with this argument... voter ID laws are state level (AKA constitutional).  Under a universal background check law everyone will need to pay for background checks, or the government will force private businesses (gun shops) to provide services (private gun transfers) for free, also not legal.  The only thing the federal government can do is set up a federal DMV style system for background checks on the private sale of guns that cross state lines... intrastate private gun sales are off limits.