I'm trying to understand what the trading costs are in ETFs and funds. Is the explanation below correct?
ETFs have trading costs because they trade almost like stocks, so you need to go through a broker to buy/sell shares, and brokers take a commission.
That means that the ETF's trading cost depend on the broker you use, no on the financial firm that manages the ETF to track its respective index. E.g. you could buy a Vanguard ETF through a broker that doesn't work in Vanguard. Thus, this fee has to do with the broker, not with the ETF itself, therefore you won't see it in the ETF's prospectus.
On the other hand, funds don't trade like stocks. Investors can buy fund's participations directly without the need for a broker, which discards brokers commissions. However, the fund in question could take a fee for this kind of operations, though this is not usual. In any case, this hypothetical fee is totally related with the fund, and you should be able to detect it in its prospectus.