I have a 5906 (had a couple actually). They are a fantastic workhorse of a pistol. The price in my world is fine at $350. As far as trading the PF9 I doubt you will get $150. The LGS I use if very up frnt on trades. Book value at condition of gun X 60% or .6...so a used PF9 is worth about $200 at .6 = $120.
So maybe you can get the $150.
To add to what what others have posted I have a 5906..it's a great service (open) carry, trail, truck, home defense gun. I don't try to CC with it.
I carry a SW 659/6906,(SS/Alloy) 459/4506, (Blued SS/ Alloy)(Double stack) SW CS9 & .45, SW 3913 and 4513TSW all single stacks. All can be bought for $450 to $250 depending on which you like.
I carry all of them in a rotation as well as a Sig P239 in 357 sig.
My favorites at you price point
is the 3913 and 659 or 6906. 659 is just a slightly older version of the 6906. The 6906 & 5906 were mfg concurrently.
My absolute favorites are the SW4513TSW and the Sig P239.. because I like bigger bangs