I used regular quartz aquarium gravel topped with an inch of vermiculite, and then topped with HD play sand. I filled a 180 for under 50 bucks. The biggest problem I had was disturbing the vermiculite layer when I re-planted, and also you do get some layer mixing if you slope the substrate, especially with loaches in the mix. I went that route because I was running out of funds in the set-up, end result is that the plants grow fabulously. In the past I have always used flourite,but the biggest tank then was a 32, so money didn't matter so much. If I had more moola, I would have used flourite or EC in the 180 too, but I was going broke, so researched other options.
http://aqualandpetsplus.com/Plant,%20Vermiculite.htm
Even though it looks a mess in the pics in the link above, my tank doesn't look like that. I don't gravel vac. Would I use vermiculite again? For the dollars saved in a big tank, yes. In a small tank, no. If you use it, you do need to plan ahead, though.