truck/mechanic troubles

[niko]

10 days ago my f250 broke down on the way home from codfishing. it was stuttering most of the way home and got worse as we got closer to home. my gearhead fishing buddy seemed to think it was a fuel delivery problem. i had it towed to my cousins shop the next morning and he thought it was the fuel pump. it made sense and he swapped out the pump and fuel filter. the fuel system was stll only pumping at 35 psi (it supposed to be 55psi, i'm told). it still wouldn't run. up until now no idiot lights had come on, but now the check engine light came on and my tranny o/drive light started flashing. the mech read the codes and said a bunch of things came up so he started doing them. he changed plugs, replaced a sensor in the rearend, checked the fuel regulator - still not running. he said he wanted to try a few more things and i agreed to let him have the truck for 1 more day. now the question is what to do about the bill. he's my cousin and my tenant. i feel like he didn't fix anything, replaced a bunch of parts that probably didn't need to be replaced and is going to try and whack me w/ a big bill. plus he still has my boat to get ready for spring. on top of that i'm going to have to bring the truck to the dealer - cha-ching! how should i handle my cousin's bill?