I would say aim for a free ETF which TD Ameritrade offers otherwise the trade fee will kill your principal!
Also, the amount you put in is barely a blip on the radar. Look to how you might be able to put aside more money to push in to this retirement account.
A lot more details would be necessary regarding income, expenses, savings etc.
Maybe try a case study in the general forum with more details on your situation to get more general advice on how to improve your savings rate and increase your principal! It's a good start down the right path though!