Not super hard to do yourself, depending on how long they are and how straight you can cut. If you do decide to cut them yourself, buy a GOOD pair of hair scissors that you use for this purpose only. Seriously, I cut and permed (OK, aging myself a little here) from 8th grade through high school and got compliments all the time (even from strangers.) So, I am not trying to discount professionals, but a bang trim is not really hard in most cases.
If you do decide to do it yourself, error on the side of having to trim again by cutting a little at a time instead of cutting too much at first. Also, the biggest pitfall that people fall into is continually trying to correct/straighten their bangs until they are too short... oh, a little bit here, oops, now a little bit here, etc, until a little bit has turned into a lot of bit.
That being said, check around, my salon will schedule in a 15-min $10* bang trim. (Not much different than going in to get your brows done.) Talk to your stylist also; she/he may have other suggestions for extending the in-between time.
*or less depending on how much often you go there, I can pop in for free... but that probably means I spend too much there.
Then again, I've been going to the same stylist (who now owns the salon) for about 10 years.