oil pump is dead, need help!!

ok, my sister has a 2.3l that is making about 20psi of oil pressure at idle and when you rev it, the oil pressure drops....so says the shop its at. i have a 5.0 so not familiar with the 2.3 at all. it needs a new oil pump and the shop wants almost $800 which is way more then she can afford. i do all the work on my own car but like i said, i dont know anything about her car. how hard is it to change out the oil pump? its at the shop now so i cant even look at it to see how hard it would be to pull the pan down. if its like my 5.0 i know the k member runs right through the middle of the pan and the pan wraps around the k member making it a nightmare to do. any help would be great guys, thanks

it was advised to me that i should try to do an oil change since the engine only has 70k miles on it orriginal and was a show car for a while. they said maybe the oil filter is clogged. i put in a new filter and some good oil. started the motor and at first it sounded like rockers knocking but then all of a sudden the oil gauge went from the red up to the half way mark. i would think that this is where it should be. do you guys know where the oil sender is, i cant seem to find it anywhere. im not exactly sure what it looks like and my haynes manual wasnt much help. i want to hook up a mechanical gauge and test it with the fresh oil and filter. also eliminate the gauge as "reliable" if its not.