Stop spending!!!
Hmmm... save your money. I promise you, it's something with your bass. First and foremost, finding a great bass sound comes from the fingers. If your bass player isn't good, then finding a good bass sound to sit in the mix will be impossible! Second(this will make all the difference), adjust your pickup height to make sure you can hear each string. If the pickups are too close to the strings, you'll have a fat sound, but all mud, back it off just the right amount so that every sting becomes distinguishable from the other, and make sure that volume levels are consistent across all the strings. Backing the pickup too far away from the strings will just make your bass sound thin. Third, fresh strings! Get yourself some fresh strings, stretch them, intonate, and if they sound "too fresh (bright)" pick up some Johnsons paste wax at a local hardware store. Apply a very thin film to an old t-shirt, buff into your strings. A little dab does it, but it adds that perfect "two days" later sound to your strings. And if you're super anal, pick up a can of food grade silicon spray for your stings and back of your neck to speed the neck up a bit.
Now, try going direct! Your recorded bass sound should be thinner than in a live situation. Bass in a mix is more about midrange, not necessarily low end. And if it sounds too forward in the mix, send your direct signal to an amp for re-amping and play around with mic positions to add some distance.
Please, please, please save your money. Great gear can make the difference between this year's grammy and Dark Side of the Moon, but if the engineer/mixer isn't great to begin with, the best gear in the world won't save you. Take time learning your gear first, and then when it's the gear holding you back, upgrade. Hope this helps. =)