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I use a ring spanner from below and use a ratchet strap that I wrap around the passenger side wheel with the strap's hook through the other end of the ring spanner. Easy.

That allows two hands to...

Do it from the top, breaker bar with a long bottle jack handle over that for extra leverage is what I used to do. Piss easy.

Have a look on ebay. They have a range of Nissan Key blanks with either fobs or the remote built in. You would still have to have the blank cut and the key's NATS chip coded before it will work. ...

Sounds about right my new remote cast me $90 from memory and he coded it for me for nothing
some charge an extra $100, that was from a dealership