100 for a mantis is alot IMO.
I bought mine at Island Pets here for 39.99 and he was at least 6"...
Most LFS get them in as pests and then put them up for sale as a bonus.
Some LFS will actually order them in, this is where you get overcharged though and likely what happened if you paid 100 for one.
Check around this site, you'll see high quality live rock for 3/4$ a pound here.
I would bet you could get 300 for your setup, as long as the tank is in good shape and all the lighting and fans still function.
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