I'd source all the parts at the best possible price, and then fork out for the repair. Though a 126 is not 'worth' that much, to their owners, they certainly are, and if you intended to keep the car for a long time, by forking out you would end up with a nice rebuilt/restored example, buying you much more time to enjoy it.
Don't think of it as an investment, just a good old friend.
Alternatively you could source another 126, but it would probably end up costing you a similar amount (or perhaps a fair bit less), but would have none of the sentimental attachment and history you have shared with your ciaoflyer.