This comic from The Oatmeal says it all:
Sorry folks, but “exposure” is not a valid form of currency.
If someone is good enough to do the work for you,
and what they produce is good enough for you to use,
then it’s good enough to pay them with real currency.
Simple as that.
And a pro-tip for all you “creative” types (artist, designers, developers, engineers, and even trades peoples) – usually when someone says to you “it will be good for exposure”, they are the last person to spread the word offer referrals.
Ask me how I know.
Whether you have been doing your work for 2 months, 2 years or 20 years, your time, effort and skills are worth real money if someone is prepared to use what you produce.