Glass or stainless steel would be better, the latter having the advantage of being virtually unbreakable, the former having arguably superior acid (but not alkali) resistance. You'll be fine this once, though! Yours will likeliest be either HDPE or polypropylene (PP). There may be code marking which will help you to establish this. PP would have a number 5 marked on it (probably, but I never quite trust the cheap stuff!)

Stainless steel funnels can typically be found in the canning section of stores that have canning sections, for a quite reasonable price. I have three, each suited to different purposes.