In GSAM battery-monitor, Tasker typically takes between 7% and 20% of my total battery usage.
That's a big number, but it does not concern me because:
1 - I have boatloads of profiles and widgets doing things that (as you say) by their nature would tend to consume power. I rely heavily on Tasker so I don't have to use a lot of other programs for these functions.
2 - A lot of the things I do with Tasker save power. For example turning wifi off when I leave home. Turning display rotate on only for certain applications (so I don't have to leave it on continuously).
3 - I enjoy the control that Tasker provides... having the phone act exactly the way I want it to.
How you structure your profiles (particularly conditions of your contexts) will make a lot of differences. See
Tasker for Android
Internally, Tasker does its best to keep power usage down. Following are some macro-strategies to achieve this.
When a profile contains multiple contexts, power is saved by only monitoring for changes in order of the least-power-hungry first. For example, in a profile with a Time and App context, Tasker will not decide that it needs to monitor for a changing application unless the Time context is active (because the profile cannot become active until both contexts are active).
Tasker rates contexts for power-hungriness in the following (ascending) order:
Day / Time
Calendar Entry State
Cell Near State
Wifi Near State
Proximity Sensor / Gesture Event / Orientation State (accelerometer activation)
Items at the bottom of the list won't become eligible for monitoring until all items further up the list are active.
So, try to stay away from things near the bottom of the list For example use cell near in preference to wifi near. Having your phone respond to certain shaking gesture may be "cute", but it'll cost you dearly to have Tasker continuously keep accelerometer monitoring for that gesture. And if you're using a high-power context, ADD a low power context to minimize it's impact.... yes adding another context can SAVE power (if the added context is lower power type) because Tasker monitors the lowest-power context and if that context isn't satisfied it doesn't bother monitoring the high power context. Also consider adding Display on as context so things that aren't important other than when you are looking at your phone won't take power while phone screen is off. This reduces the number of times you do the task. Also it costs less power to do a task when the phone is already awake then it does to wake the phone to do a task.
Also you can adjust monitoring frequecies in the monitoring tab of tasker settings.
If you are curious about effects of Tasker and about your battery usage in general, I'd highly recommend GSAM battery monitor. Seems much more straightforward than Better Battery Stats and seems to have a wider range of accessible/understandable stats reported (BBS gives you tons of info but what does it mean is not as clear). Once in awhile a program will jump out of the ordinary and you learn something by observing that. For example, I used to use Tasker to "kill" a certain program (Chroma Doz). I observed that on two occasions Chroma Doz kept using ridiculous amounts of power after it was killed. Apparently it doesn't like being killed. So I removed that action from Tasker and do it manually now.
If you have been making a lot of changes to your Tasker profiles, you might keep an eye out for unexpected behavior (things running too much) by occasionally checking the active profiles (listed in the notification bar profile and in %PACTIVE) as well as running tasks (listed in %TRUN)