Why not Viva?

I travel a lot to other border cities and the best bet is to take an official airport taxi to the border (done that in Reynosa, Matamoros and Tijuana before CBX)
It will likely be expensive like $20 USD
Pedestrian Crossings: It depends on time of the day. I've done 5 minute to hours. Global Entry has no benefit. You'll need MXN coins to pay for the crossing. 5-10MXN

Bonus: I see Uber has service and tried to quote from CJS to ELP and it works for $7 USD. You might want to try that one