Nitrogen to fill shocks near Gresham OR

Looking to put 200psi back into my race runner front shocks. Looking for a shop that has the equipment to do this. Was hearing a knock on the drivers side and checked the pressure and it was less than 30psi. Hopefully it isn’t toast! It’s a 99 and these were added before the fire department took ownership when purchased new so they have been used. I have had it about a year and didn’t hear this to begin with. Hopefully it just needs to be refilled. Any idea on what I should expect on prices? Thanks, Troy