prices haven't gone up on games in the last 5 years. in fact, i can remember paying 65$ for some new releases in the past, whereas lately 55$ is the max.
if you can't afford to "comfortably" spend 55$ on a video game, you ought to look into cutting back spending in other worthless areas (learn how to COOK for example), or find a higher paying job.
also, i bet it cost upwards of $100 million to produce doom 3 over the last 5 years. 55$ is not too much to ask for that amount of man hours. and they've got to fund this and other projects.