Sub-surface Laser Engraving won't work with CO2 lasers as acrylic is totally opaque at 10.6 μm. The machines that can do it use 530nm pulsed lasers with servo controlled focus for the depth. They typically run around $20K or more.
Frequency is something to keep in mind when building your own engraver too. There's dirt-cheap solid state lasers up to like 10W on eBay. While they'll work great for wood, they're useless on acrylic and glass as the 400-500nm beam passes right through. CO2 really is the workhorse because its infrared beam is compatible with so many materials and you get a lot of power for the $$$. Think my last 80W tube cost me $320 shipped from China.