Individuals can rarely obtain the prices operators can for air, hotel and meals. Aside from quality considerations, remember their pricing includes the cost of advertising, guides, overhead and profit. Many tours include little organized and in-depth sightseeing in the starting price. Basic tour prices are very competitive, often priced below actual cost. Yet, the operator must profit somewhere.
Options are the usual path to profit.
These may well be things you want to do. You should understand in advance how much you'll likely spend on excursions and how that cost compares to what you can do on your own. Not at all, but something you may want to keep in mind as you tour. There are two factors to the success of a tour - the operator, and the guide. You can, and should, check out the operator in advance.