While I won't pretend to be a doctor, I feel confident enough from experience to say that taking almost any expired drug is not any more dangerous than one fresh from the pharmacy. It may, however, be less effective, but that depends on how it's been stored.
In general, heat, light and humidity gradually cause most drugs to break down, which is why it often says on the label "store in a cool, dry place." However, drugs are not like food - it doesn't go moldy, spoil and poison you just because it's beyond the expiration date. I wouldn't eat canned tuna that was 3 years beyond its expiration date, but I wouldn't hesitate to take a drug that old if it was all I had available and I needed it.
Now, whether or not it's a good idea for you to be taking pred at all is quite another question. I can't answer that. Pred is generally quite effective, but the side effects can be severe, and the longer you take it, the greater the risk. You've taken it before, so I assume you already know how it affects you. Possibly there is another drug that might be better, possibly you are in need of surgery, but probably (from what you've said) you can't afford those options. At the end of the day, it's your call. And I wish I could be more helpful.