Last year, my neighbor, bought a new, Sears, gas string trimmer--and it came with a drive chuck to fit a drill driver, and allow you to start it, just as was mentioned, like a race car. It also came with different cutting heads, and ground-traveling wheels, for about $125.-150., IIRC.
However, the performance of the cutting head was pretty abysmal. By that I mean, LONG GRASS WOUND UP AROUND THE HEAD, within 2 minutes, and took us FIVE MINUTES, to clear, with tools (screw driver and needle nose pliers).
And it happened again, and again, and AGAIN.
I've used weedeaters for 30 years, and I've NEVER seen one get SO tangled, so fast, with long grass wrapped around the shaft.
While I believe he could find a better brand cutting head, and it might even fit right out of the box, that's a maybe, and would probably cost another $35., with no guarantee that it would solve the problem (which I feel is due to there being too much exposed [rotating] shaft, between the tube housing, and the cutting head, itself).
My point is: the drill driver starter option worked like a charm, and is inexpensive.
But I would look for it elsewhere--you couldn't GIVE me his weedeater, given the above "wrapping" problems.
Thanks for the info on the battery-powered stuff--I was not aware it existed.
My Hoe