Tim, 750 feet is considered a very short distance to run a buried airline. Depending on the number of diffusers and the CFM required to properly aerate your pond you "may" end up using 5/8 ID direct burial line to the pond edge and then 1/2 inch ID from there.5/8 line should cost you less than $15.00 per 100ft. (Lowes Home Depot type stores)Bill C. is correct on having power pondside as it comes in very handy at times.You may want to consider trenching in for the airline(s) and dropping a 10or12-2 UF with ground in at the same time and have the best of both worlds.(code permiting)Have done this many times) It is also easier to set the valves on a multiple diffuser setup if it is pondside. Figure about 4-5 amps to run a pair of diffusers on low volt.Good Luck
