So if I want to get in on this game I will need to purchase this pack with the 300i - https://robertsspaceindustries.com/pledge/Packages/300i
And then the 5 dollar arena module?
Well as he said, you could get the Aurora, although it's not particularly good at combat or racing. But it's the cheapest package that comes with an Arena Commander pass: https://robertsspaceindustries.com/pledge/Packages/Arena-Commander-Starter
Another option is to get the other starter ship, the Mustang Alpha: https://robertsspaceindustries.com/pledge/Packages/Mustang-Alpha It's a little better at fighting, but it doesn't come with Arena Commander access, so you'll have to buy the $5 pass. Combined it ends up costing $5 more than the Aurora package with AC access above.
Then you've got the cheapest 300i package that Daedardus suggested: https://robertsspaceindustries.com/pledge/Packages/300i It doesn't come with an AC pass either, so after you get that for $5, you end up spending $25 more than the Aurora package above.
You can pretty much do this with Star Citizen all day, spending $5 or $10 more to get a little fancier-looking ship, until all of a sudden you've spent $500 and you're wondering how long you'll be able to stand the taste of ramen noodles. But keep in mind that any package* you pledge for comes with the full game in the end. The Arena Commander pass is just to pay server costs for letting you play stuff now.
*OK, except this one, which only gives you Squadron 42 (single-player campaign) and not Star Citizen, it looks like: https://robertsspaceindustries.com/pledge/Packages/Aurora-MR