You probably don't need a cage right away - unless you're mounting a lot of accessories or doing a lot of handheld it's just decorative. If you do think you need one, I prefer the smallrig cages - they're more fitted and generally high quality.
Start with the Rode VideoMicro - around $50 and it's a really good on-camera mic. You can buy a 1/8" stereo extension cable and mount it on a boom, as well. Eventually you'll want to add something else, depending on what you're filming, but the VideoMicro is something you'll keep finding a use for.
It's hard to find a good, smooth, inexpensive tripod - generally it's "pick two". I'd really suggest upping your budget and getting something like a Manfrotto BeFree Live. Keep an eye out and you can find them on sale for around $170, sometimes a bit less ($150ish). It's a travel tripod with a decent video head that is small/light enough to be easily portable. Even if/when you move to something heavier you will likely keep it around as a travel tripod.
If you can't up your tripod budget, Davis and Sanford make some OK budget tripods. This one has good reviews:
It's going to be heavy, but heavy = stability and smoothness with tripods (to a degree).
I tend to recommend everyone get a decent tripod starting out, you'll be glad you have one. Yes, you can hand-hold, but that is a definite style/look that doesn't work for everything. Learn to frame up and do basic camera moves (pan, tilt, etc) on the tripod, then practive the same thing handheld.