While George makes a good point, keep in mind that the lower the control voltage, the higher the amperage required to pull in the relay. With a 55kw motor, at 460vac, you are looking at a size 4 starter or larger. I've seen a size 2 (yes, in poor condition) draw 22 amps on the starter coil on pull in. It blew a 5 amp fuse like a flash bulb !! A large 24vdc or 24vac relay with a rating of at least 10 amps on the contacts should be okay with a new starter. If the starter is questionable, I'd look for a relay with a 20 amp contact rating. I wouldn't, in any way, connect the starter coil directly to the PLC output. A larger relay might, in itself draw to much at 24v.... Whichever, put protection on your PLC output in the way of a fuse and/or spike protection.
Like George says, a $20-$30 relay is a lot cheaper than the PLC....