Welcome to the DH side.
The Navy is serviceable but few of the upgrades can be added to it, if you want a DH to dive the DA is a much better choice. I have no idea what Bryan charges for servicing one but I can give you a general cost of parts to get it back in diving shape. You will need to replace the hose loop (hoses, mouthpiece and cage valves), main diaphragm, put a service kit in it and replace the duckbill. Rough numbers, that's about just shy of $200. To that list I would add new hose clamps, a band clamp , a duckbill eliminator (instead of the DB above) and a hookah port adapter....roughly another $50. The majority of the cost is replacing the old rubber parts, that is almost a one time thing since the new silicone replacements last a very long time. While you might get away with reusing the old rubber parts, I highly recommend not using them unless the goal it to keep it as original as possible. Reguardless of how they look and feel, they are no where near as good as the silicone replacements and frankly, I hate the taste of the old rubber mouthpieces. If diving it is the objective and not "restoring" it to original look, the new DSV hose loop would be a good choice. Mouthpieces are a personal choice (assuming you are not trying to keep it original looking). Personally, I dislike the straight one- it's too big to be comfortable for me. My choice for a reg I dive a lot is the Voit hourglass design, I find it the most comfortable of the rubber(silicone) replacements.
From there, you can do a lot of modifications to improve the performance if you like. All of the mods are bolt on so they do not damage to regulator, it can be returned to original by simply returning the old (style) parts and most of the mods can be added one at a time or all at once.
There is a very active group of us here who rebuild, restore and dive these regulators so help and assistance is easy to find, just ask.