Oh, sure, what's another head job
No big deal to do it when you need to do the timing belt anyway. My Subaru shop even has a package deal. Not kidding. Cheap too. I could do both in my garage in a weekend and the package was cheap enough I wouldn't bother. Just let 'em do it.
That's definitely true for a new car, but for a $1000 Prizm, the economics change. 400 gal to break even isn't insurmountable at all.
Insurance costs are a wash. You had it on the old vehicle, too.
So you're going with 400 * 2.5.
40 / 20 MPG ... 2 gallons.
40 / 40 MPG ... 1 gallon.
It's going to take over a year just to break even on fuel alone.
Insurance: You aren't going to remove insurance on the gas guzzler are you? You're keeping both vehicles right? Annual licensing fees? Taxes? Initial sales tax?
I would guestimate (and keeping in mind that we own six vehicles and three trailers, and I keep good records on every penny spend on the "fleet") that you'll hit true break-even around 3 years in.
A $1000 beater will need some sort of major repair at a minimum of $500 at least once in those three years and that'll reset the break even out another year.
You can make it slightly less painful if you do absolutely all work on them yourself, and already have the tools or consider their purchase not part of the net/net cost of the fleet.
Little problems will also crop up on the vehicle that sits unused more often.
Not trying to talk you out of your dream of commuting in a POS. It'll be great.
(Mine aren't down to the $1000 POS quality level yet, but I won't be keeping them that long. I'll let them get old, but not ugly or poorly maintained. Well actually one isn't running but it's a bigger project to rebuild a TV remote truck into something else...)
You aren't going to save any appreciable money for roughly three years. You'll need something better than the $1000 one to make it make any sense and then the recovery cost horizon pushes out to five years.
It's a money waster until it pays for itself. No getting around that with a "fleet".