Go for Roland. It appears you only want to use it once or twice - hence renting? If you can't rent one and want a low cost solution - Roland JV1010. World Expansion is great for erhu; Orchestral Expansion is excellent for flute. Problem is JV1010 only fits one expansion card. But if you can live with the build-in flute in JV1010, then it's fine. Unless you are talking about the Chinese flute (Dizi or Xiao), then the World Expansion card will do.
If you want to go higher cost, go for any of the XV modules. Then get the expansion cards.
If you want to go for ultra-realism - then go samples. Best chinese instrument samples on planet earth comes from Chineekong. Their website seems to be down now - for whatever reasons. Anymore realistic than that, you have to get a real player.
What keyboard are you using currently?