Don't let price be your only guide when buying a converter. There are valid reasons why there can be big differences in converter prices and from looking at the outside you can't tell why this would be. There are many internal parts that could be custom made. My previous employer for example could put in a custom built steel stator, anti ballooning plate on the pump cover, use a custom steel mounting cover, depending on the customers needs.
Find out what each company is offering you for the dollars they want for their product and go from there.
I've seen enough converters apart to see why some are more expensive than others.
