So, a couple months back, I bought a really cheap used bass (seems like a '62 P-Bass knockoff, 'Racing USA' brand), and soon after, a cheap Ibanez 15w amp. I really started to get into bass, I'm looking for bands now, and I know I'm gonna have to upgrade soon. So, knowing these facts, if I only had one to upgrade, what should it be? Price range is between $300-$400. List good products/brands.