I'd rather advice on spending $20 on an Altcoin. Much less effort and more potential return, since several days of mining will probably return a few dollars of current value.
I wouldn't underestimate the effort of buying new Altcoins, especially with dollars. If you already own bitcoin it is easier, but buying new altcoins requires that you go through potentially untrustworthy channels on smaller exchanges as new exchanges generally won't have them available.
