Since this is not what you do for a living, you need to ask yourself a few questions.
1. moving the dirt is not a problem, have you driven 200 ft with your BX, lets say at least 20 times in a row without stopping? The BX is not known for its ground speed efficiency. You noticed I rounded up the footage driven since you will need it for driving around pile, maneuvering obstacles and such. With BX, it will wear you down quick, so this being said a BXpanded bucket extender is GONNA help! Every little bit will make a difference. Do you have a trailer you could use too ? With right setup, you can load trailer, hook up trailer, drive to location, disconnect , lift with bucket to dump, go back to pile and repeat. all of this can be done without getting out tractor with 3 pt hitch.
2. Are you doing this on your vacation time from regular work? will you be able to replace your "lost vacation time" with same rate of wages? This is typically the going rate you charge. OR are you doing this on a weekend for diesel money plus a little extra for your self just to get the job?
3. insurance, breakdowns? If something happens, are you prepared for the risks? Do you have a time line you must complete the work within?
4. I wouldn't worry about the cost of getting BXpanded extender if it something you can use at home too. If it a one time use for your client, and no other jobs lined up in future, just three truckloads? well I'd say its a borderline decision. by the 3rd truck load or so, you will be either be kicking yourself, or be proud of what you done without it.
Usually when people ask me do to things for them that require use of my tractor,fuel for both towing it there and tractor, I give them a few hundred dollars quote just for my time and the work to be done if it can be done in one day they always (99 percent of time) give me a little extra which is nice. Your mileage may vary.