We've been using Low Doller Motorsport sensors on our racepak, happy with them so far. They are a way cheaper alternative to the plug 'n play branded v-net sensor but have to be used via a universal serial module (USM). Some low doller sensors may need the calibration table inputting but as far as I can tell, the majority are like for like.
One advantage of data logging over a go-pro is you can overlay runs and see if your adjustment / tweak, has made any improvement to that particular parameter during the next pass and if it has helped 60ft / et / mph etc.
I would keep an eye out on the various racing websites as a lot of Data logging stuff comes up for sale and can be had cheaper than new but there's obviously the S/H caveat. I've found support for Racepak real good here in England, appears to be the most popular logging system used and the various websites / forums are pretty good too for help and info.