The watt meter most of us use is the cycle analyst from ebikes.ca, it's an essential piece of kit to be honest and it tells you stuff like consumption per mile, current amps which is useful if you want to know if you are being too hard on your motor and battery.
There are a few different types, one is called the direct plug in, it connects to the controller and you can adjust your amp limits and speed. The other is the stand alone that can't limit speed or current.
I think you are going to have a hard time building a 30 mph system on 700 USD ?
Say 500 USD for cell-man's 8T 1000 watt high power kit including shipping. That leaves you only 200 for the battery!
If you get 9 of these http://www.hobbyking.com/hobbyking/stor ... ouse_.html
That would give you 55 volts and 15ah or 23 miles range at about 35 watt hours per mile 25-30 mph
This shows 435 USD shipped to Ireland so I'm sure it would be cheaper for you. But you got to then spend more on a balance charger and power supply, probably looking at another 200+ Euro's!
Then you have to make cable harness to connect all the batteries together, and you can't store LiPo in your house and you have to take good care of it and constantly monitor each cell voltage, for which you will have to spend more on cell monitors.
You should check out the battery section, there is lots of information on LiPo and that will tell you what you are getting into.
Study them well and don't rush into buying anything until you are fully confident you can look after LiPo!
This battery from cell-man is 550 usd + shippinghttp://www.emissions-free.com/catalog/i28.html
I'm sure he could make you up a 15 ah pack ??? obviously it will cost more. Going with LiFeP04 means it will be bigger and heavier than the LiPo but you just plug it in and forget about cell monitoring and it will last a lot longer than LiPo. You should get several years out of that pack!
With just under 12ah with the emissions free battery you might just about make your 30 km commute, if that's both ways ? if not you will have to charge at work!
There are other LiFeP04 packs but their discharge rates are too low for the mac kit and that's why I recommend cell-mans LiFeP04 packs, I think you would need a little more ah so you could ask him to make a 15ah pack ?
Unfortunately there is no way to go 30 mph for 30 kms that is going to be cheap!
If you are prepared to pedal a bit the 11.5ah pack from cell-man is the best way to go!
Back to pedal only power.