The AI should always value constructors and colony ships pretty high, unless there are no more colonizable planets. If it doesn't, you buy its entire fleet of constructors for a couple techs for no admins, and it loses admins. It also had values warships too cheaply before, but a bit too expensive now. Before the nerf, you could buy every warship every AI owned for practically nothing, and the only thing that stopped you was maintenance costs, which some techs can stop.
The root of the problem is that the AI doesn't know how to individually value each ship like a human does. It doesn't even put starbases in the right spot, and skips precursor relics all the time. If it doesn't understand those basic things, it has no idea how to value a ship. It also shouldn't be having a lot of constructors built sitting around doing nothing, but it oftentimes does.
But in general, an early game constructor or colony ship should be worth somewhere north of 1kbc or more, and warships should be priced according to era, where as tech advances, older ships get a bit cheaper, and the newest ships worth a pretty good amount. Of course, exact values would have to be tweaked and there would likely always be exploits when dealing with AI.