Hi N2g, I was just kidding about the editing. Guess I'll have to learn to use the smiley faces. Please don't hesitate to disagree with me. Many ESL students have learned things I've never thought about.
Okay, you're right, "as he drives etc." is a clause, but I wouldn't say it's independent. IMHO it functions as an adverb, modifying the verb of the main clause, "are burning up" (as I said previously). Sorry I missed that it's a clause, but I think my point is still intact.
Yes, there are three independent factors effecting him financially, and the price of gas is only one of them. Unfortunately, "gas prices" is the subject of the main clause.
This is what the sentence is supposed to say: "Gas prices are burning up his paycheck." Okay?
The problem is, you have a modifying phrase preceding that, and you have a modifying clause following that. The phrase at the beginning modifies the subject, "gas prices." The clause at the end modifies the verb, "are burning up." But, these two modifiers set up an impossible conflict. You can have one, or the other, but not both.
The prepositional phrase at the beginning adds the other two factors to the subject, "gas prices."
Now we have, "Three things are burning up his paycheck." No problem! That makes sense.
Let's back up and take the other route. Forget the cost of food and the shrinking hours. Instead, let's add on the verb modifier, "as he drives, etc." Now we have, "Gas prices are burning up his paycheck as he drives etc." No problem! That makes sense.
But, what happens when we try to add the front modifier and the back modifier at the same time?
Is the cost of food burning up his paycheck as he drives? Heck, no!
Are his shrinking hours burning up his paycheck as he drives? Heck, no!
This doesn't bother you? It sure bothers me. It makes no sense.
Best wishes, - A.