You can get better than OEM speakers for $40-50 a pair. I always recommend crutchfield because its easy to use, they have filters your specific vehicle and they have great support. You can always start there, and do a search to see if you can save a little somewhere else (usually amazon). A quick look showed me about 15 pairs that were $40-$50 with low wattage that will work well with a factory head unit, or if your budget will allow it, a new head unit. If you look on the website, the only ones I would avoid (under $50) are the Memphis because of the paper woofer.
If you want to do it as cheap as you can with something a little better, I would pick just one pair, (really, any pair will do better than OEM). Cheap speakers is just one of the sacrafices car companies make to bring the production cost down. Those who care, will go big, and that's all relative from there. Base level factory speakers are meant to be basic.
You can pick up a used head unit from the normal places for less than $50 that will give you more options, and a few more watts than the factory. If your budget allows it I would get a second matching pair for the rear doors. You can find some small speakers to replace the ones in the back, but it doesn't sound like that's priority.
Last, of course, depending on your budget, and time frame, black Friday is coming up. I would expect to save some then. On ebay you can find some decent package deals for a pair of speakers and a head unit for $100-$150, again sounds like it depends on your budget and what your goals are.