I think people are missing the point of why he didnt save the slave-
1) new world, new rules. Hes been here less than a day. For all he knows this is the norm and he would be an idiot for trying to change the status quo
2) hes broke. that pocket change will buy him 1 night at a 2 star inn, wheras an elf will probably cost him a years worth of life savings if the cliche holds