Not too many 2009-2010 1.8L owners here and even less who have done any performance modifications.
K&N makes a short ram air intake that will work. My mom and I both have K&N SRIs on our 2009 Vibe GTs and have been very happy with them. I'm sure the one for the 1.8L would be just as good. I also have a Magnaflow catback exhaust system on mine. Unfortunately Magnaflow doesn’t make a direct fit system for the 2009-2010 1.8L Base Vibe / Matrix, but you should be able to find an exhaust shop near you that could fabricate a custom setup for you for a reasonable price.
Hott Exhaust is a great place to get Magnaflow products. Their prices are unbeatable, they offer free shipping to the US and Canada and there’s a link on their homepage to message them for discount codes. Click the link, tell them what product/s you’re interested in and they’ll send you a discount code to save you even more money.
If you haven’t already, I would highly recommend checking out
Matrix Owners. From what I have seen, there are a lot more 2009+ 1.8L owners over there who have modified their vehicles and should be able to provide even more information for you. Keep us updated on any modifications you end up doing to your Vibe and be sure to make a post in the Vibe Lounge introducing yourself and your Vibe. Also, be sure to add some pictures of your Vibe because we love pictures around here

!
P.S. I know you're wanting inexpensive modification ideas, but if you happen to win the lottery or something you could always
turbocharge your Vibe 
!