Clothes for an active lifestyle - quality of quantity?

I've never spent more than $5 for a pair of pants. My parents have bought me a few pairs for birthdays that probably hit $20, but in general, there wasn't much point in spending that much - what I didn't outgrow, I usually outlived.

I wear through clothes like a diarrhetic porcupine through a roll of TP. Some might apply the verb "trash" to my clothes usage, and it wouldn't be a big stretch. I've been aware of this for a while, so when I shop thrift stores I always look for the most rugged, durable-looking jeans in my size range... but they still wear out! And its not like I'm usually even doing anything crazy like sliding down rough granite or wrestling wolverines. The last pair of jeans I broke tore on a beach! The one before? Swing dancing!

Anyways, I'm in the process of sorting through all my personal belonging in preparation for my move to Florida, and I've come across a dilemma. Yesterday I sorted and packed all my "stuff", today comes my wardrobe. Fortunately, I've been planning for a transient early-adulthood lifestyle for a while now, so I don't have too much to work through in either category. I've realized, however, that I need to make some adjustments to my selection of trousers. The internship description for the farm I'll be working at starting in July recommends bringing "lightweight work clothes," "modest shorts," khakis for giving tours and some "nice clothes" for attending churches or conferences. As most of my pants currently are of the $5 don't-quite-fit-cause-I-bought-them-at-a-thrift-store variety, and none of them could be considered "lightweight" (important in FL's humid summers), its time for some exchanges. I can think of several options:

1. Keep the pants I have that are comfy or in good shape, and augment them with further thrift store purchases as these wear out. (We'll call this the 20x$5 option)
2. Invest in several pairs of decent pants that won't last much longer than thrift store pants, but at least will fit well and be of a lightweight material. (5x$20)
3. Research heavily and choose just one or two "ideal" pairs of pants, ones that are convertible, ultra-rugged, fit well, dry quickly, and look good. (something along the lines of this) (1x$100)

The advantage of options 1 and 2 is that I have a certain degree of flexibility in choosing a pair of pants in the morning. On the other hand, with option 3 some degree of flexibility is built in, and I have 4-96 less pairs of pants to shop for and cart around. There is a certain risk you run by putting all your money in one pot though, so perhaps option 2 is a good compromise.

In general, I prefer 1 of something that does the job well to 3 of something that do the job less well. It costs fewer resources (though not always money) and simplifies moving, cleaning, and organizing. But with my track record with clothes and everyone else's preference that the color of my pants doesn't clash with my T-shirts, is it worth it here? Thoughts?