If you own 1000 ETH, you pay 10 ETH in fee for fast speed transaction, if you own 100 ETH you pay 1 ETH fee, if you own 10 ETH you pay 0.1 ETH.
In stock market, poor people pay the highest trading fee, where rich people pay low trading fee, 401k probably paid zero trading fee because they own the brokering market, yup, stock market benefit rich people and punish poor people on trading fee alone.
Transaction fee depends on what platform you are going to use. There are platforms that has fixed transaction fee and there are also platforms that are basing your tf on bitcoin's current price value and the amount you are going to process. I think there's no specific percentage on ETH as well. You can adjust the transaction fee depending on the wallet you are using, but always keep in mind that too much low transaction fee can lead to slow and even unprocessed transactions.
In my experience, those platforms that has fixed tf process much faster than those of that you can adjust. The miners prioritized the transactions of those who paid higher. In simpler manner, you can refer to those who pay higher tf as VIP's. The higher the tf, the faster the speed of transactions to be processed.
Regarding stock market, there's no use to compare it to bitcoin since we know for a fact that stocks are centralized and are regulated by the government (especifically SEC) while bitcoin is decentralize in nature. There are brokers in stock market which has to be paid by the investors while in cryptocurrency, there are only wallets and networks.