2007 nissan muranoawd replace or repair engine?

Bought 2007 nissan murano awd $6000 and $1000 to register.
Two months later hardly drove it I now have a blown head gasket with oil in
my radiator. Got screwed from the get go and has been nothing but a money
pit to me since.
Has been sitting since before xmas because i dont know what to do. Dont
have funds to go buy another car as i am a new widow and times have been
really tough for me.
I do know how to do basic mechanical work not afraid to get dirty but this
problem is bigger then my knowledge.
The car is like brand new on the inside with all the bells and whistles and the
outside is good with nothing major body wise. I was offered $750.00 as is
with bad engine. I cant take that hit.
Question... Do i replace engine with rebuilt or used or do I fix head gasket
and hope block isnt cracked and take the chance?
Is it worth it to fix it?
Its got i believe 120,000 miles on it and i drive half mountain half freeway
alot so i need a reliable car. i just am at a lose and dont have a clue what to
do!!!
At this point i hate the car and rather i have been driving my 2003 chevy
avalanche beat down with 260,000 miles and am much happier at this point
but would rather use that for my winter driving while its still going and not put
the mileage on it if i dont have to.
PLEASE someone tell me what to do, whats my best option or not and if not
how do i get out from under this hell car with out losing what little I have?
And if i fix it do i do the head gasket or replace engine? And if I replace
engine di I go with a rebuilt or a used one? I dont know what to do next!!!
HELP PLEASE!!!!! i would be internally great full for any input anyone can
give me.
Thank you and stay healthy!