Not guilty or guilty? didn't have my registration or license on me, but both are valid, what do i plead?

i got pulled over for not having my seatbelt on and i didn't have either my license or registration on me. the office looked me up, said both were valid but ticketed me for not having them on me... it's 180 freakin dollars!!! PLUS a 49 dollar seatbelt ticket! i have MANDATORY court tomorrow even though ON the ticket it just has a court date, no box checked that i must appear, but in the letter they sent--it said i have to go or else i will have a warrant and/or my license will be suspended. i do NOT want to pay $180 for the registration/license ticket, if i bring both in should i plead not guilty or should i just plead guilty and ask for them to lower the fine or what? i mean, i guess i AM guilty of not having either on me but i still don't want to pay 180 bucks..