Tequila Not Made From Cacktus!!

All tequilas are not the same.

Tequila is made from distilled sap from hearts (piñas) of the agave or maguey (pr. 'mah-gay') plant. This plant is a succulent actually related to the lily and amaryllis (it has its own genus, Agave). Although it sometimes shares a common habitat with many cacti, it is not one itself and has a different life cycle.
A mature blue agave has leaves 5-8 feet tall, and is 7-12 feet in diameter, measured from leaf-tip to leaf-tip. It has a lifespan of 8-15 years. Other species have longer or shorter lives, depending on growing conditions and climate. The name agave comes from the Greek word for 'noble.'

                                         There are 136 species of agave in Mexico, of which the blue agave - agave tequilana weber azul - is the only one allowed for use in tequila production. Several different species of agave are allowed for use in mezcal, including a rare wild species, tobala. Other agave plants are used for the production of various regional drinks like sotol, raicilla, bacanora and pulque. Agave has been cultivated on this continent for at least 9,000 years. (THE HARVEST OF AGAVE)

No commercial Mexican alcoholic drink is made from cactus.
However, cactus is used in some fruit drinks, salads and other food items. A popular cactus used for food is known as nopales. It's tasty and quite healthy.
Price isn't always a good way to judge things. A lot of the cost may go to fancy packaging, designer bottles, large advertising campaigns and simply to status. A well-advertised and promoted brand selling for $100 USD or more is not necessarily a better buy than an inexpensive 100% agave brand at $30. It depends on your taste and what you expect in a tequila, as well as the care and attention the producer gives to the product.
There's a large selection of excellent tequilas available in Mexico at $30-$60 USD, and a very good choice in the range from $60-$100 USD. Under $30, most of the tequilas are mass produced for the local market, and usually mixto (not 100% agave). Above that price, they're aiming mostly at the export and premium-status market, often with collectible bottles and recently introduced individually numbered bottles. Some premium brands are not even sold in Mexico, only in the US or another export market.
Taste is the ultimate deciding factor and each person's taste is individual, personal and changes with what you eat, how you feel and the time of the day. Some people prefer the rougher edge of the young blanco tequilas with their more distinct agave flavour. Others like the more mellow, but still sharp flavour of a reposado. And some may prefer the smooth, woody aroma in an añejo. Try them first at a local bar, then decide which to buy.
Like single-malt scotches, or small-brewery sakes, tequilas vary according to the company making them, the process, the plants and their growing environment. The temperature, soil, types of equipment, age of the plants, how and when they are harvested, the means by which the plants are baked, and the way the tequila is aged all affect the flavour and body.
There is a surprisingly wide variation in tequila flavours - especially between styles like blanco, reposado and añejo - making it difficult for many neophytes to recognize each distinction, especially when the more subtle añejo tequilas are involved. There are also regional differences. Tequilas can accost you, confront you and challenge you - or they can woo you or seduce you with soft, subtle fragrances and dusky aromas.
Production techniques affect the taste. Generally traditional methods produce much stronger agave flavour than modern, mass production. Aging in barrels also affects the taste, and not always to the better. The woody flavour imparted by the oak can overpower the natural agave.
Fancy packaging, wooden boxes and elegant bottles - many handmade or decorated by artisans - and are now common with premium tequilas. They have become collectors' items in their own right and even empty bottles can command a fair price on eBay. While they don't add to the basic quality of the drink in the bottle, they do add to its charm and certainly its visual appeal.

Source: http://www.ianchadwick.com/tequila/myths.htm