Yeah I think TBME is more toxic, but the decision to use that over diethyl ether was not mine, I don't pay the bills, but I don't think the price difference is massive (I had a quick poke around on sigma-aldrich). Our solvent storage tanks are above ground, I have no idea of the disposal costs, it goes into the non-chlorinated waste tank with all the rest of them, and the department takes it from there. A significant proportion of the chemistry we do in our group is aqueous, so this cuts down overall toxic solvent use - although I'm not trying to use this as an excuse, I'm following workup procedures developed by the group and from papers that is my reason for using the solvents I use.