Games Workshop's moonscape pack is a pretty good value. For under $20 dollars and well under two hours’ time, you can have five nicely detailed 40k terrain craters. These craters are multi-functional.
They can be used in the bombing Planetstrike to reflect the pre-game and storms of fire, and they can be used in any Warhammer 40k game to show where tanks or castle explodes. You can also purchase discounted warhammer models online.
In terms of the game and players are subject to the agreement, craters typically deliver 6 + or sometimes cover 5 + save as field area. They may or may not be considered difficult terrain, again depending on the wishes of the players.
The craters paint up very nicely right out of the package. Their prime and then the base coat in earth tones, followed by a lighter color on the paint, and highlight by dry brushing light shade. It will look fantastic.
You can pick up the crater to a higher level, however. You can mount or support crater on durable MDF Formica or other. You can add rocks and gravel into the crater to make each of them more unique and more detailed.
Glue sand, gravel, and stones (made of polystyrene) for each of them to make them more unique and detailed. Prime and paint as described above for the base of the crater. You can finish by painting up the battlefield detritus you as you do your army of miniature to 40k and gluing them to the crater.