For instance a mirror ball effect is great for the slow dances. Lighting upgrades are usually packaged together with sound upgrades. The most common sound upgrade is bi-amping. First, the sound will be very crisp and clear, and second, the music is louder. For large venues accommodating over 300 guests, a bi-amped sound system is optimal.
Professional DJs charge accordingly.
If you find a DJ charges more than their competitors, ask them why. And of course if you encounter a DJ charging significantly more or less than their competitors, I anticipate you will know why. One or more of the above questions will tell you why there are price differences. During the time that you book a DJ, you will need to reach them. Knowing they are available full-time without additional costs to you is comforting.