I have 1-3 months to devote to something online, what?

I would start a few websites, add a load of unique content get some backlinks built up then in 3 months sell them as semi established sites providing 2-3 months traffic/revenue stats. Depending on how well the sites are doing you can flog the site for $xx-$xxx each
I would say maximum 3 sites otherwise you will end up being too thinly spread and maybe even get the 3 sites linked like a mini network.
Or just do the blog and flog it in a few months

 

You could look at becoming domain name reseller. No initial sign-up cost.

You need to book a domain name, sign up for reseller account and set up private labeled website. See example. Setting up the site took me less than 15mins. Then onwards you can take care of your business and make profits, while backend processing is taken care of completely. Your work would be more to receive payments from your customers and add it to their funds.

This whole thing can be done in 1 day. Rest of the 89 days you need to devote to marketing and taking care of customers that sign-up at your site. You can provide end-user accounts or make more resellers under you.

This can fetch you money in long term.

You can sign-up here, if interested or PM me for further details.