A few options you have.
Some people get the cases repaired. if they are repairable, pictures can help us determine that.
It all depends on what you can find, and price. If you can find a whole bottom end or a engine for under $200.
Then it might be better to go that route.
Cases, what I have seen, is used without damaged going from $60-$75 per side. a whole set around $100 to $125 without damage.
It all depends on timing and luck of a deal.
A aluiminum local welder, might be able to fix them. here in my area, they charge $85 a hour. But felt he could fix it in 30 minutes. not including grinding it back to spec.
Someone on here charges $50 per case (you have two cases). not bad, just the shipping to him, ect.
Whats your ability ? if you can afford to buy a good running motor, you mgith want to do that, if you dont mind some wrench time and have a good understanding of what you need to do.
Have you split the cases yet ? checked the tolerances on the crank / rod bearing ?
Seems like, piston / rings range from $50 to $120, depending on what you get. then you got gaskets and seals. $40 plus.
bore and hone job, $50.
then the case issue, if nothing else is needed. $100 to $150.
so you could be looking at $300 +.
Use that ruff number and see if you cant find a good bottom end or whole more.
There are people on here who have good parts. im sure they will chime in or pm you.
I have heard the if you do not change the jetting, when riding in the winter, it causes it to run lean !
the 2001 blaster we have, the previous owner was riding in the winter, when they blew it up. same situation / out come, you have.
I just rebuilt it a few weeks ago and been working on another blaster and motor.
Sporty