Technically construction is possible to get completely for free, while summoning actually requires that you spend gp with an npc to level up. So in that respect summoning is the only skill in game that you must spend gp on. However. comparing the usual method of cons.. it omes out far more expensive. Remember that you can sell and alch pouches to redeem a small amount of your money back.

 

Con... turning logs into planks requires money to a npc

I think con. Since with summoning you don't spent money on charms, you get them (you only spend money on pouches and spirit shards)