XXCycles has the Stronglight in 110 BCD up to 52T, for $17. More 110 BCD, 5 arm, Shimano-compatible chainrings here. I purchased my TA chainrings from XXCycles. It shipped fairly fast (about 2 weeks), and XXCycles had the TA chainrings in black, whereas from the US sources, I could only get silver. Stronglight are reputed very good chainrings, and XXCycles are about the only place that has all their offerings.

The Stronglight Time Trial chainring (which looks stiffer, to make up for the smaller spider), up to 54t.



These chainrings might well be worth a try with the Sugino crank you have, as you'll have other components to replace, such as RD, cassette, etc. If they don't work out for whatever reason, then you can opt for the crankset.