ok well vacation for a couple of weeks ,you can use dosing pumps for that.
after the first couple of months pass, then the system would mature, and less dosing is necessary ... so you can get away with just dosing the carbon source using a dosing pump or a friend to dose it once a day for you.
as for expense ... of course its extra cost, but you will be able to get away with lower water changes, and no po4 remover ! so you save on those.
for a 100Gallon system, you will use 30ml of Zeostart3, 10-15 ml bak, and about the same amount of Sponge power PER MONTH. plus carbon and zeolith exchange every month
so you can calculate the yearly cost from that.
that is the bottom line ... the least amount of supplements, you can also use other additives later on which add to the cost.
HTH,