An important thing to remember is that in blockbuster trades non-stars are just filler to make the money right unless they are young prospects. I'm getting that out of the way to give you an idea in the disparity of trade value between stars and regular starters.

The best way to know a player's value relies on 4 main factors imo, in order: (1) talent (2) direction the franchise owning the contract wants to go (3) cap hit vs. talent gained/lost by team in trade (4) years left on his contract.

Since 1, 2 and 4 are fairly straightforward concepts of weighing cost/benefit I'll just explain (2) - direction team is headed.

Tanking teams will generally try to trade any player teams are interested in that aren't part of the team's rebuilding plans. Kent Bazemore on the Hawks is a good example - he was originally signed when the Hawks were aiming to make the playoffs and he is a serviceable SG, but he's too much older than the rest of the Hawks' young core so he is more than expendable. A rebuilding team will try to gain as much draft capital as possible from their expiring and/or non-essential contracts generally at a fair cost.

Middling playoff teams will try to fill need without annihilating their draft capital while shedding bad contracts when the price is right.

Contenders will often trade away as many picks and young prospects as they need to if it means that they have a great chance for a title. Young players won't fit that timeline if they are not already stars so that's why you see teams like the Lakers being so willing to trade away Ingram, Ball, Kuzma, etc.

For the purposes of this year's deadline I would just say that most expiring contracts will just be dealt for 2nd round picks and 1 or 2 bad contracts will be traded to tanking teams with a good draft pick attached. Tough to say how any of the blockbuster trades will go.