With me it's all a matter of pronunciation. Collectable sounds right. Note that it can be used as a noun or verb adjective. Again it depends on where you live. This is what Wikipedia says about it.
Spelling
Although "collectable" is the spelling listed first for the adjective by the Oxford English Dictionary and is standard spelling in British English, the dictionary observes that the "-ible" form is also valid, and has come to be common spelling in the United States.
My pronounciation treats the 'a' and the 'i' as the same sound.
'Pro-nounce-iation', or 'pro-nun-ciation'? Tomato, tomato.