Question about transaction fees in trading

Hello dear binancers,

I have a question regarding transaction fees.

And I am not talking about the exchange commisions.

With fees, I mean the fee to use the blockchain itself. Like gas in ethereum for example. Each blockchain has its own method but all of them require to pay a fee to interact with the blockchain. And as far as I know, when I trade BUSD for ETH, for example, I am interacting both with the BUSD blockchain and with the ETH blockchain, to take coins out of one wallet and put coins into the other wallet.

I know that for example ONE has incredibly low fees, so yeah, it won't matter if I buy 300 coins or 3000. Fees will be more or less the same. Binance gets a 0.1% commission because I am VIP0 and trade via BUSD instead of BNB.

But I wonder what goes on with ETH. If I want to buy let's say 100 BUSD in ETH... can I predict the transaction fee? Because I've read that ETH is very expensive to do transactions. So if I will pay like 20 BUSD to buy 100 BUSD... then it's probably better to wait to have more cash and buy 2000 BUSD. I will lose money if I trade small amounts.

But the thing that confuses me is, how can I not predict at least an estimate of the fee when setting orders?

Do this kind of fees not apply for trading?