Invest in better speakers or a subwoofer for car audio?

Hi guys, I'm in a bit of a pinch. I really want to upgrade my car audio, but I'm kind of on a budget. I'm trying to upgrade my car audio for under $150. Yeah, I already know I can't get GREAT sounding speakers or a subwoofer setup for under 150. I get that. So I'm going to make a choice. Should I invest in upgrading the speakers of my car? I have a Honda Accord 2008 EX model, without navigation or dual climate control and with 6 speakers. Or, should I invest in a subwoofer setup. A note about subwoofers, I DO like the low end that you can get from subwoofers, but I'm not a bass maniac where I need my car rumbling from the bass. I ONLY care for the presence that subwoofers give. I'm adding this because, although I'm not sure, there are probably car speakers that have really small subwoofers in them, and all together they give pretty great low end, but I'm not sure about that. I'd really like your opinions on this, and again, I know you can't get super great car audio for under 150, but I'd like to make do with what I can get.

Thanks in advance!