This might help contextualize the project:

A previous state report speculated that construction may cost $42 billion in 2017 dollars. That sum should be considered low until proven otherwise, in light of the 0% engineering; the soaring costs for California’s high-speed rail program, whose ultimate San Francisco-Los Angeles network could reach $128 billion; and process delays in Seattle’s own Sound Transit 3, whose $11 billion Ballard-Sodo light-rail segment won’t complete preliminary engineering until 2026, a full decade after voters approved higher taxes.

If planning could help prevent mistakes and delays costing something on the order of years and billions of dollars, half a billion to plan (1% of a lower-end estimated cost) doesn't seem so bad to me at all.