What size tank are you plumbing? IMO, unless you are running a full siphon drain, you do not "need" a single valve in your system. You could get away with only two unions if you position them correctly.
On my old 40B, I had non collapsible tubing for the drain and dual 3/4" returns. Probably had more money in various nipples and adapters than I did in pipe costs.
Bigger sizes like 1-1/2" is where the fitting costs are considerably more as Chris stated above.