A mini-ITX motherboard is just as capable as a micro-ATX board. The principal difference is the number of expansion slots. If you're building something that doesn't need more than 1 expansion card then mini-ITX will be fine.
Smaller does not mean cheaper as you've already found out if you look at the price difference between your 2120T and a 2120. Most mini-ITX motherboards tend to be more expensive than the micro-ATX counterpart.
Without knowing anything about what you plan to do with this system
(hint, hint). I would match the 2120T with an ASUS P8H61-I motherboard, one or two 4GB Kingston low-profile DDR3 1333 memory sticks, a 128GB SSD and one of these cases (which depends on if you need an ODD or not):http://www.ecosmartpc.com/ei5.htmlhttp://www.ecosmartpc.com/ei7.html
If you want to use more "regular sized" parts (PSU, ODD, 3.5" HDD) the Lian-Li PC-Q07 or PC-Q11 are nice mini-tower PC cases that take a mini-ITX motherboard.