used engine how much does mileage matter ?

Hi, we were driving from VA to FL in our 2007 Nissan Altima when the engine suddenly blew out without any warning lights/noises, in GA.

Never had any problem with it before and had taken it to have an oil change the day before and was told we needed to have the battery cleaned, which we agreed to; when we stopped in NC and again in SC both times car wouldn't start so we had to get it jump started even though we never had a problem with that before either.

We now have to have a used engine installed (old one blew at bottom they said it overheated but don't know why) we have been quoted $1300 for one thats 96k miles & $1475 for 63k miles, both with 1 year warranty, seems obvious to me to get the 63K one but I wondered if it makes that much difference and whether there is some formula or sliding scale for how much it should cost with reference to milkeage ?

Total cost with $1300 one, with labor is $3400 +tax - expensive but Altima seemed in good condition before this.
Wondered what people thought about this, I have no clue :dunno: it makes much difference as these engines are supposed to do 200K easily I was once told.
Thanks Chrissy