Pretty much any weapon type u decide to skill on gets rather pricey as ur get into the higher skilled weapons.
I found laser pistol was pretty cheap up to the p5a, laser rifles get pretty pricey right after the breer m4a, and swords get pricey even sooner, after the embra sword ur looking at +1k peds just to get SIB.
Now what weapon u use purely depends on ur own personal preferences.
But some pointers...
If u like to team hunt alot do not skill melee as it is very useless in a team hunt when everyone else has a gun.
If ur interested in getting ur attributes uo like strength and stuff then melee is def the way to go.
One last tip. if ur caught between blp and laser, hard choice to make and im sure many will have their opinion on this but i suggest laser, as it has alittle more variety in being able to use amps that are not rediculously priced like Blp. Tho blp does sound way cooler!
my 2 pec
fyi i dont have a main weapon i skill all weapon types minus heavy weapons.