Let's say you triple your subscriber count. Your monthly cost for 4500 subscribers would be:
Mailchimp - $50/month
Campayn - $25/month
iContact - $47/month
How many hours would it take you to build something yourself? Plugins won't cut it, apart from setting up Wordpress forms. How much is your time worth?
Well it really depends on what you need, but since you said that you've just started an internship, you'll probably want something you can get started with quickly without much hassle, and you'd probably want something affordable.
If you're not looking for an expensive, full fledged CRM with an overabundance of features that you will never use, I'd suggest you go with something like CampaignMonitor, Campayn or Aweber.
If you want a better reply, you'll need to provide more details.
I'm one of the people behind http://campayn.com, an email marketing service.
We give you the tools you need to design, send and track your email newsletters. We are specifically geared towards small businesses, and we're rolling out new features every month.
If you come from here during this week, hit us up on our support email, and I'll set you up with extended premium reporting and/or a few months free for one of the premium plans.
Name / URL: Campayn
Elevator Pitch: Email Marketing should be simpler, easier and more affordable while still retaining all the important features. We are working on making this happen.
Right now we're working on expanding to other marketing niches and adding more international languages to the system. Stay tuned!
Feedback is always welcome, and we're looking for partners for other international markets. Right now we have Germany and Portugal/Brazil covered, and we need people that can handle translations, marketing and support for new markets.
If you're coming from reddit, shoot support an email and I'll make sure you get 6 months of free premium reporting on the free account plan, if you decide to try us out!