Went to the parts store and they told me a ngk iridium....doesnt sound right to me. Its just a base model 04 grand prix gt1 non supercharged....if it is, is there and acceptable (cheaper) alternative

OE were acdelco platinum , when gm changed things they went to using NGL plugs and iridium

NGK Iridiums are good plugs. Autolite makes a cheaper alternative if you go Iridium as well.

iv been looking and o'reillys has a pretty good price on Champion double platinum...that's what i have in my sunfire and it runs like a champ...is there any mechanical or reason theyre using iridium?

Use the OEM plugs. Ive sold a bunch of people cheaper plugs (coppers or platinums instead of iridiums) because they get sticker shock, and at least half of the time theyre back for more parts or different plugs because the car runs @!#$tier.

GM designed it that way for a reason. Unless your boosting or using spray there isnt a reason to use anything else.