! This is all my personal opinion, so take it with a grain of salt. !
When something inside a car engine breaks that requires it to be torn apart, there are only two economical options:
1) Buy a new car
2) Buy a new engine to put into the car
Having an engine rebuilt is almost never worth the money spent, unless replacement engines are prohibitively expensive due to scarcity. The only way to come out ahead rebuilding an engine is if you have the tools, skills, and free time to do it yourself. And even then, the odds are not in your favor once you get around to adding up the costs of new pistons, valves, miscellaneous seals, gaskets, and so on.
Between the two options listed above, #2 is only viable if your mechanic is extremely trustworthy: a family member or a very good friend. Engine replacement is not for the amateur, there are too many corners to cut and things to forget that can cause serious problems later on.
For a ~$2000 car, I don't think I would bother with an engine replacement.
Now I'm going to suggest that perhaps you don't need a backup vehicle and the considerable expenses that such a luxury incurs... insurance, registration, repairs, gasoline, maintenance, and so on...
1) Does your husband really need to drive to the train station a few miles away? Is he not physically able to bicycle there?
2) Driving in to work... how far away? Within bicycling distance? Is carpooling not an option? Is the primary car in use every single day? If you have two separate jobs, can you move closer to one of them? Or better yet one of you change jobs closer to home or at least near one another so you can carpool?
Not trying to be a douche, just planting ideas in your head. This is MMM's forum and I'm reasonably certain that if he happened to be within earshot of a phrase like "backup vehicle," there would be some faces a-gettin' punched.