Guns are given their prices for a reason. Their attachments aren't considered when setting prices, it is purely the stats. People just expect every gun to perform the exact same way. It's like expecting a shotgun to compete with an assault rifle. They can both be good in their own right just in different situations.

DSR is around 100k if I remember, it is a high freeze/ slow firing gun that deals high damage. So given that what other gun is like that? the PBP.
So then you compare their stats.

DSR has a 4 clip, can kill in 4 shots, has 0.37 freeze and 0.43 firerate for 100k.
PBP has a 5 clip, can kill in 4 shots, has 0.4 freeze and 0.4 firerate for 125k.

As you can see both are quite similar, DSR actually has a slight advantage as unlike the PBP, it fires one bullet that does the 14-15 damage or whatever it is. PBP only deals its full damage if you hit all of the bullets which can only really be done if you are up close.

PBP is still a very popular pk weapon, so considering the DSR is quite similar, and cheaper, I don't know how you can justify it needing to be given something to make it more appealing when its stats speak for itself.