Logic Puzzle – Crossing a Desert

You can do 1 porter at the beginning for 1 day (can only take 1 lb first day, send him home with 2 days; will have 1 day left over) and 1 porter at the end for 1 day (only need to take 1 day from him too and will have 1 day left over). 4 + (4-3) + (4-3) = 6 days supplies. Its 4 porter-days worth of salaries.

You can do 1 porter at the beginning for 1 day and 1 porter at the end for 1 day. 4 + (4-2) + (4-2) = 6 days.

I think you just need one porter for 2 days. After 2 days you take his supply and continue the trip alone, with a supply of 2 x 2 days.
(I know, the porter won't like it this way but it fulfills the requirements AND it is the cheapest plan. And it's not for real anyway. And also, maybe these porters have got a satellite phone to contact the office in case of emergency.)

No, they are not paid to get home. They get to keep any food supply that is not needed for their return trip.

Are you allowed to have 1 porter start from your destination and meet you part way? If so, I believe 2 porters for 2 days, each with 3 days food would work.

You take 4 days food and start the journey with 1 porter carrying 3 days worth of food. At the end of day 1, each of you has consumed 1 day's food. He splits his remaining food, restoring you to a 4 day supply while maintaining 1 day's worth of food for his return trip.

You have the second porter start out from your destination on day 4, 2 days before you are scheduled to arrive. He also takes enough food for 3 days. He consumes one day's worth travelling to meet you. You meet him at the end of day five as your food runs out and he has enough for 2 more days. He provides your final day of food and completes the journey with you on day six.