Disguises and Fancy Duds

AC is pretty good right?
We can use this in more ways than we thought.

A thief asks to make a disguise to do... whatever. How much time and effort and gold is he going to put into this disguise? A few hours and roughly  enough gold to buy some chain mail? Right, the DC on seeing through his disguise is now 16.

Here's how I'd do it, given that this is completely untested.

Take the table of prices for armour.

For each chunk of time (1 hour, 4 hours, 1 day, whatever is most appropriate) you move up a rung towards plate mail.
If you pay enough gold for your rung's equivalent armour, you can keep it as your disguise DC. If you don't pay, move down rungs; one if you pay more than half, two if you pay less than half. Move up rungs depending on your disguise skill, if that's something your game has.
The rung you end up on is your equivalent disguise armour.
You can use the stats exactly as written.

Why is it so heavy? Eh, clothes are heavy sometimes, but I also I think it could represent the kinds of "empty spaces" in clothes that are expected for your disguises. You wouldn't expect a priest/noble/beggar's clothes to be bulging with loot/equipment.
Why would it give you disadvantage on stealth (if that is a thing your armour does)? Same kind of reason, the clothes you need to wear might be heavy, or dingly, or otherwise not helpful for sneaking in.
Why does it mean you have disadvantage against shocking grasp spells? Okay, look smart-arse, why don't you put some thought into it and apply your common sense instead?

We could also easily apply this to Fancy Clothes too. Fanciness is a protection (or insulation at least) against a good few things sometimes, especially if parties are a thing your uh... party go to.

A good disguise/set of fancy duds could be as valuable as armour in certain games. It could be a money sink for people who don't need plate mail. And I think it adds something to the discussion of "What do you mean I can't wear my owl-bear-stained plate armour to see the king? Why do I need to look good for nobles?" and also the "What do you mean I can't immediately disguise myself as an archbishop in ten minutes with only a set of face paint and bravado?"

Though that last one does actually sound like it can only end well.