A question like this is like asking “How long is string?” And thus I would say that it depends. The fact that you want to engrave wood, crystal and acrylic lends itself to using a laser engraver as opposed to a traditional rotary style engraver. I have often felt that while traditional rotary engravers have their place in the engraving world, lasers have more flexibility when it comes to different materials and substrates. Most laser manufactures have table-top entry-level CO2 lasers which should work within your parameters. I suspect the lower-wattage models such as 15 – 25 watt lasers should suffice for your requirements and budget. But once you find a laser which fits into your budget, remember you will have to factor in an exhaust system and software to run the laser.