Well let's see, assuming you're going nuts and are willing to blow all three of your possible Restricted Gear uses on just your commlink, under standard creation rules:
Singularity Battle Buddy Basic (comes with armor, hardening, and biometric lock) 10,000
Response Upgrade 7 24,000 [this assume you're GM will let you start with a rating 7 anything]
Response Enhancer 5 10,000
Simsense Accelerator 15,000
Optimization (whatever your focus is) 500
Customized Interface 250
So... 63,750 as an implanted commlink (you could go higher with various widget accessories, but you'll be getting little out of it and you'll just be asking for GM ire) and in addition to nyuen you've used up 15 BP on restricted gear and .2 essence. For .04 essence you can half that price and make it secondhand. Is that unprecedented discount in cyberware terms? Quickly skim the core book... and... no. Retinal Duplication (Rating 6) is 90,000 nyuen and .2 essense... so .04 more essence saves you 45,000 nyuen buying it secondhand and you've only blown 5 BP for Restricted Gear to get it.
Of course, pairing the above hypothetical secondhand commlink implant with a secondhand simsense booster makes for some descent hot-sim VR initiative (14 + Intuition) and passes (5) for less than 70,000 nyuen.