Riding (potentially) 30 miles a week is not that much (I don't mean for this to
sound mean or snobby, I'm just saying...), if everything on that bike
basically works, it would likely be worth putting a set of tires on it. I
agree that I wouldn't bother putting new hardware on it, but the
general-maintenance items are not that expensive and may be worth it, if it's
the only thing keeping you from riding. If you don't have a
bike co-op in your area (I don't, sadly), then talk to your local LBS or check
your local sporting good stores. If you search, you should be able to find a
27" tire for under $20, maybe under $15, without too much difficulty. This is
not an "upgrade" to the bike, it is making it safe to ride (also, you can get a
new chain and cables,both, for well under $20 at Walmart). If things are so
tight that a $30-40 total is going to burden you, then buy one at a time.
Overall, that's the price of a (small) tank of gasoline. How quick do you think
you'd be able to recoup that amount by riding your bike vs. using your car?
Then, you're in the black and can save toward your next bike.