What the hell are you working on?

[J.E_Magog]

You need to know what type of paint was on the model.
1. acrylic - methyl spirit or windex will do the job nicely
2. Enamel - mineral turpentine (Shouldn't melt the plastic, but you should always test this first.)
3. lacquer Mr color thinner or brake fluid will do the job but they are quite expensive.(you have to soak the model in the brake fluid)

Do a bit more research before spending more money.