I am looking to make an offer on my first investment property. It is an REO, cash-only, single-family home. My question is, do I need an agent to write my offer or is this something I could do myself.

It is something that you could do yourself but why would you want to? The seller pays your agent costs so you won't be saving anything by offering on it without an agent. 

REOs typically have an online system to submit offers. The link to thisnis typically found in the agent to agent remarks in the mls. It is unlikely the reo agent will even return your call. They can not get both ends of the deal. So without your own agent you are unlikely to even get your offer in.

No, you can not write your own offer. You need an agent. Also, there will be bank addendums which void out/change out a lot of the terms in the required local realtor contracts. This is not s DIY project.

Hi Amanda, Most REO/Asset Managers will not look at your offer if it is not presented correctly. In the meantime, someone else might buy it from underneath you.

It will not add a penny to the purchase price to use an agent. You can either use the bank's agent who is listing the house or find your own.  And if you want to buy just this one house and never speak to the agent again, that's something you can make clear.  You are not tied down whichever  agent you pick.  Just this deal. 

Best of luck