hiring people only when we need

we are a start up and we have to make a decision on how to deal when we have to write any documents/presentation(technical/marketing/pps/etc).
Let's say by instance that I have been contacted by a client that would like to have us to create a concept and a general overview of a product they would like to buy or get implemented from scratch by our company.
Now we could create those documents our-self but, because we are not English mother-tongue, we are concerned about the result that may be not professional enough.
We are thinking to pay someone every time we need a document/pps/etc. for a potential client instead of doing it our self with the risk that the client may refuse to collaborate with us perhaps because the document does not give them the perception we are a good company

what would you suggest?

What's the best resource for hiring people every time me need to create documents?

Please do not look for a third person to read your mind and come up with a fancy document. What you know about your strength and capabilities, that third person will never be able to articulate.

What you can do is, hire a visually creative person one time and ask him to come with some professional looking templates for document and powerpoint. You can then use these templates every time you need to respond to one of your client.

BTW your English seems to be good enough. Don't worry about it not being your mother tongue.

Did you consider hiring a resource from sites like Elance, ODesk, vWorker. You may find good resources there.

I would suggest you hire a native English speaker or contact a translation company (you can do it on-line) and ask them to correct your English documents. You are supposed to be responsible for your concepts and ideas you're going to sell. You can't rely on somebody else to do it for you.