Are you only interested in LV ones? Tiffany makes some cute solid gold charms with diamonds, that are the same price as the LV ones which are only in "golden coated metal". (500 ish$)
Have you thought of using a twilly/scarf to tie as a bow to it? It adds a nice pop of color and is quite cheap, since you can find a twilly for 30-50 $ on sale.
I use any charms I like. Swarovski, Coach and Micheal Kors have nice charms. I also saw some cute charms today at H&M. They only reason I didn't pick one up was because I was afraid it may cheapen the look of my LV. I also found a pretty vintage large gold pendant that I attached a chain to that I use. There are many less expensive options for bag charms. My favourite so far are LV Bandeau's. They are about $140 but beautiful silk and made in Italy. I love the way they look tied on the bags.
I started a thread awhile back about how we decorate our LV's. If you click on my name, you can see the threads I've started and you should be able to find it. I'm not sure how to link it up to this post. HTH
For a pop of color, I typically use a bandeau but have been using my multicolore pastilles charm lately. I love all those pastel colors. I also have a bright orange Graffiti charm that I use once in a while --I've seen a few of those lately--pre-loved on the bay/bonz---for about $225-250 though.
For less than $100--you could do Juicy or Coach. Or even get an LV Luggage tag with your initials--you could do the initials with a bright color like blue. They're about $52 with tax.
You purchase them at the LV boutique, and just ask to have it heat stamped. They usually ask you to wait around for 15 minutes while they heat stamp it.