How to invoice outsourced translations for my client?

I have a copywriting and content creation business as a sole proprietor I've been doing full time for the last 3-4 years. I have a return global B2B client who I've been helping with creating their content that is now requesting to have some translations done - for now just 1 language, could be more in the future. Currently it's 6 documents of 100-200 words each, so overall it's a very small project that could lead to more so I want to propose the pricing model properly at the get-go for my client. I am not cheap and my clients are typically global brands and I do compete with some of the bigger creative ad agencies here when it comes to content creation for them.

My question is as a small agency/sole proprietor I am that would obviously outsource this, what rate would I charge and in what model? Some of the well- reviewed translations houses I can see charge as little as 10-20 cents per word. If I use a professional directly, the rate from him/her will be a bit more.

So what kind of set up for myself and for the client would I propose? Is there a recommended or standard percentage of the translator's base rate I should then charge my client? I assume I would also charge some standard starter/project rate? What should that be? What do others do when they need to outsource a piece of content when it comes to invoicing your client.

Any advice would be much appreciated!