Your young, and prone to terrible ideas. Don't wall it--especially a c-pillar. Max dimensions would be helpful otherwise any advice doesn't mean much. Since your on a budget I would spend the money towards the cone area, and not bother with "3-4k." The difference in output likely won't be worth the investment. Especially after you factor in all the electrical upgrade costs. Provided you have adequate room I would opt for 2 18s in the cargo area, or 2 15s. If I sound harsh it's because I was in a similar position not that long ago, and I've made many vehicle alterations that I highly regret.