Cheapest solution to increase volume on RPi3

Volumio Information

Volumio Version: v 2.0
Hardware: Pi3
DAC: None

So eventually I am now using the RPi3 with Volumio to drive a set of Creative Labs PC active speakers through the 3.5 mm jack. Normally these speakers are plenty loud enough when used with a(ny) unamplified PC. Is there any way to amplify this output to a usable level without having to buy an expensive DAC hat and case to fit it? It’s just for a cheap and cheerful garage stereo.