This is a straw man argument.
The only way to lower these costs through gun control is to reduce the number of guns in circulation by 99% or more.
The cost of such a confiscation scheme would exceed the hospital costs by several orders of magnitude.
On the other hand, the hospital costs could be reduced enormously through strict enforcement of prohibited possessor law and by long sentences for violent offenders.
That cost is roughly close to the benefits realized.
When the government which has all the guns shoots you and the other dissenters, there are no medical costs...