I would say no. IMO MBP has higher resale value as current iMacs are 21.5" and 27" and with iX CPUs. Basically, the low-end iMac is faster than that 24".
I would ask him to pay a bit cash too, then it's fair if you want an iMac instead of MBP. You could just get an external monitor to make your MBP a desktop. Best of both worlds.