Is there a practical, inexpensive way to track power usage by source?
The low cost "plug-in" energy monitors are actually quite good, but are limited to devices that plug-in. As soon as you want to monitor devices that are hard-wired like your pool, spa, water heater and electric car charger, you are going to have to have something installed by a licensed electrician if you are uncomfortable with working on your household power system.

The clamp-on device shown will not show you "Power"(watts), it will only be able to show you Current, which is a COMPONENT of Power (W = V x A x Power Factor). For the devices that are only resistant heat, like your water heater and pool heater and spa heater, Power factor is 1, so you can safely estimate Power by assuming the Voltage and measuring the Current. But for the pump motors and the car charger, there will be Power Factor involved and you need specialized metering to read it correctly, otherwise you are just guessing.

A very INDIRECT way of determining consumption of any given device is to use your utility metering in the following way.


learn how to read your utility meter. Most utilities will provide you with instructions, often on a web page.
Turn EVERYTHING off in your entire house, EXCEPT the load you want
to measure
Record the Watt-Hours at the start, and again in exactly 1 hour. For the pool and spa, make sure you are doing this under the worst case scenarios; the pump is running, for example during the filter time frame, AND the heater is called for because the pool/spa cooled down. The same for the Spa. You can "force" this by turning them off for a few hours before hand (but check to see when your filter runs, often they are scheduled for off-peak hours). That energy (Watt-Hours) will give you a general idea of how much power you are using per hour of run time. 
In the case of your car charger, do the same; plug it in and turn it
on when you know that the car needs charging.


Unfortunately, you will not necessarily know exactly how many HOURS per day these things actually run. That's where a sub-metering system comes in handy. It will record the actual Watt-Hours they use in a given time frame. that takes more sophistication, hence the added cost. There are by the way some companies in some areas that own this equipment and will perform an energy audit for you for a fee, likely less than the cost of buying the equipment. In some places, like mine in California, the utility will do that for you if you ask. might be worth checking into.