With saving 3 days that's a saving of $30,000 PLUS more trips per year (a very significant factor on the ROI of purchasing a ship), so a shipping company may see a $25,000 fee as reasonable.
Operating costs of the canal would be negligable, Kra needing no locks (So I've been told, though I'm sceptical on that aspect).
A mere 10 ships each way (reasonably conservative) is $500, 000 per day, 180 million per year.
I think a decent ROI is quite feasible considering the construction costs are Thai labour and materials.
A little bit of lateral thinking such as a man-made island utilising the cuttings and becoming a business in itself (resort, sea port for R&R etc), it could work.
^ I've heard that BKK hisos behind the concept have been buying up land along the route for years. There will certainly be some urging from some quarters.
As for the OP...it's as it should be. A temporary interim government should not be concerning itself with major infrastructure. No trains, no power stations, no canals and no submarines. They should be stamping out corruption and paving the way for elections, and just that.