Ok _at lower levels_ (which is what we seem to be concentrating on at the moment) a Trader has more free IP to devote to tradeskills should he wish to.
I have a level 25 trader (to get me into the shop) and I grabbed all the nanos I could use along the way. Every level he has maxed, all base abilities, shotgun, nano int, both evades, comp lit, map nav, and I'm pretty sure every skill under nano and aiding (may not have maxed one of them) plus raised elec eng dueing the first couple of levels to equip the lamp and night goggles and I still have lots of IP left to play with (no I havent raised any tradeskill since thats not what he is there for)
An eng by comparison would have to raise most of his nano and aiding skills (for med packs, bot, pets heals, armour buffs etc) comp lit, elec eng as above, pistol (or shotgun or MA if you actually wanted to do some damage) map nav and possibly have maxed all his abilities (certainly up to level 15 anyway)
What he probably wont have is nano int and any evades if he is using trimmers (and I'm not even assuming a full 'suite' of trimmers, just a couple) as he would have to raise the skills appropriate for the trimmer use and I'm also assuming hes making his own QL30 increase agressiveness trimmer.
This also assumes he is not OE'ing on trimmers as FC basically told us we had to in out Professionals report to notice any difference.
At 25, the eng will not have any IP left to play with for 'other' tradeskills (as I said aside from the trimmer ones), unlike the Trader
At that point it doesnt really matter whos skills are cheaper if you dont have any points left.