I think you should have just asked "what's the meaning of life?" - it'd be easier to answer
If you're going to use it, how much restoration do you really want to do? 604's is beautiful! I'd be proud to own it. But he's gonna have to use it, and it'll get dirty
Just my three cents - keep your eye out for the $40 CL offering. The one's I've seen have been pretty solid - meaning burners are good. Your biggest investment would be in flavorizer bars and possibly the grates (like nice SS ones from rcplanebuyer on ebay).
Then the elbow grease.
I picked up an 1100 redhead for $30, with a tank of gas. Spent a lot of time cleaning it and re-seasoning the CI grates. That became my gasser.
Found a 2005 Genesis (stainless doors) for $20. Needed some repainting, but I was lucky, it was hardly used. Just left out in the rain.
I got to the point that I wanted a side burner.
Again, being cheap, I found a black 3000 for $25. That gave me my side burner. It even had a cover.
This is where it got fun
Took the red lid from the 1100 and moved it to the 3000. Picked up two CI griddles for it and now it's my redhead flattop. The black lid went to the 1100, which was then, via Alvin, moved down south, with new SS flavorizer bars, and is in good hands with Vwbuggin64.
The CI grates went to the '05 Genesis and is a grate cooker.
Guess that was more like four cents. Anyway, my point is that patience can play a big part in getting you to where you want to be.
And I agree with all that Golly and MartyG have said - start with solid stock, build it for yourself, and enjoy it. I enjoy mine after resto/rehab. And I'm always on the lookout for a "value priced" Summit to get me some N/S burners