Man, I hat to jump on the bandwagon, but what the hell were you thinking of when you bought the Leather armor? I can SORTA understand not buying the lvl 24 armor chainmail becuase the lvl 27 stuff is exactly the same, except not as cool looking, and 3 important levels later. It IS expensive, but it's also good for 6 hard fought levels.
In ANY case, the centurians stuff is SO much better, it isn't even funny. Some of the lvl 30 stuff can be good for up to 20 lvls, depending on your job. For instance, if you're drk, the 30 gloves that add accuracy and the belt that adds a +1 to almost EVERY stat, are great. Drk has shitty def anyway, so 1 or two added to your def here or there doesnt make a difference, but the +dex makes a big difference. Hell, your def doesn't have to be too up to date if you're anything BUT a war or pld! And you are war, correct?
If I saw your armor in my pt, I wouldnt let you tank.
I frequently accuse people of taking this game too seriously and I am more interested in having fun than anything else. However, if you were my tank, my fun would definitely be decreased because the mages would be stressed keeping you healed and the xp would blow goats. If you don't want to take the etime to earn gil, and I completely understand, pick another job that is less gil intensive. Every class has uber-items that cost a bunch, but you can get by just fine with mediocre stuff in plenty of jobs. Be a damage dealer of some sort. Like a mnk, drk, drg, or whatever where lesser items will still suck, but won't glaringly hurt your party. Every party needs 2 major things: A tank and a healer. There is no good way around that. As a tank, you are vital to your pt, and you need at least good equipment.