A "Budget Boost" is normally a set of coil spring isolators that are thicker than the stock isolators. They typically are advertised as 2-inch. This is a very affordable method of adding just a couple inches of lift to your vehicle to fit a slightly larger tire (usually a 30 or 31-inch tire).
The thing to watch for is anyone selling a budget boost for a coil spring suspension vehicle. Vehicles with coil springs in the rear CANNOT have the spacers stacked, it just simply isn't safe. They can be stacked in the front because of the bump stop "tower" that will locate the spacers but the rear only has the bump stop cup to locate the spacer, and it's only big enough for the 2" spacers.
In short, watch out for anyone selling a "Budget Boost" kit that instructs you to stack spacers in the rear (for 1997-2006 Jeep TJ Wrangler and 1993-1998 Jeep ZJ Grand Cherokee), it just simply isn't safe.