Question about fees

I've been thinking of buying into Ethereum for the last couple of weeks, but I'm confused about the fees.

I have coinbase and am new to crypto in general. I've been reading about high "gas fees". If I buy $1k worth and then decide to sell for dollars, am I going to have to pay a $100+ "gas" fee? Or am I only going to pay coinbase's 1.5ish% transaction fee?

Thanks you for your help!