Unfortunately advertising is an expensive part of doing business. I think I spent around $8000 in the first year on postcards (that's an estimate). Postage being the biggest expense. Still, in an age where everyone wants to send an emailer because it's free, you will stand out if you send tangible promos like postcards, etc.
The expense is the other reason you need to be DAMN SURE YOU ARE READY. If you aren't already getting lots of attention for you work, it might be too early. Signs you are ready are:
you are winning contests
people are sharing your work A LOT on social media
you are being asked for interviews, shows, etc
you are being asked to do actual work for clients
clients are recommending you to other clients
your instructors are saying that you are ready and encouraging you to start advertising.
If these things aren't happening, you may want to wait until they are. This is exactly what we are going to be going over in the portfolio class that starts in January.