The TwoPeas girls always have the best info for Silhouette Cameo deals. I bought mine at Overstock. I heard a lot of Amazon Prime members finding good deals using their membership. OhMyCrafts always has decent prices but apparently they are having some shipment issue last I heard.
I would buy an extra blade and an extra mat. Other things you will want to get-
Spatula to remove your die cuts from the mat. You can buy one made for die cutters. The best ones are art paint palette knives or the cake decorating knives.
Dental Pick or a tool like it so you can remove the intricate pieces off your mat without damaging the designs. This is good for lthe lace patterns that are popular right now. I use a dental pick and an awl.
Baby Wipes to clean your mat.
QuiltBastingSpray to make your mats tacky again when they start losing their stickiness.
Gift card to scrape the paper bits left over when you remove your design. A ruler also works well for large areas.
Glue Pen to adhre your detailed images. Die cutting girls like the Xyron 150 (X) also. You can also use a toothpick with Aleene's tacky glue.
A small pair of cuticle scissors or trimmer to snip those tiny pieces that don't get cut. It happens with all the machines on certain cuts.
Reverse Action Tweezers to lay your cuts down on your paper. Trust me on this one it's a lifesaver.
I learned this great tip the other day to align your cuts perfectly- Magic Mesh as “transfer film” for paper projects « Clever Someday.
Those are the items I keep in my die cutting tool arsenal. Congrats on your Cameo.