You can't skip 3 Star equipment. (Tier 3 refers to depths, which is something entirely different from armor.)

Find equipment in the wiki that you like that has a crafting line from 2 to 5 stars. Then purchase a 2 start item and upgrade it along the crafting line. Note that some beginner's equipment goes from 1 to 3 stars then the line ends, avoid that equipment if you can since it is a dead end.

Some people sell 4 and 5 star equipment on the Auction House, but it is very overpriced because in most cases that equipment had to be unbound to be sold.

dude. I don't think you mean tier 3. There are only 3 tiers in this game. I think you mean stars. Gear can can be 0-5*. All 4* recipes require a 3* item heated to level 5 to craft. You can purchase 4* and 5* items, but they will cost a ton due to the high cost of unbinding 4* and 5* items.

It is not cost effect to buy 4* or 5* items unless you are rich and looking for a certain UV.

If you have 2* armor. Figure out if the armor you have is upgradable to 5* armor that you would like to have. If so, buy the 3* recipe and upgrade as soon as possible. 3* recipes don't need any heat so you are better off doing as soon as possible.

Please see this post:

http://forums.spiralknights.com/en/node/31049

and do some wiki research.

There are also some great armor lines (gunslinger, angelic) that start at 3-star. If you plan to use a gun often, gunslinger is a great set to own. Angelic is decent shadow armor and at 5* you get different upgrade options. Crown/Armor of the Fallen is pretty popular.