information regarding investment/return is awfully hard to come by i have found (particularly as we are restricted to the newbie area).
my advice would be to start here -
https://github.com/litecoin-project/litecoin/wiki/Mining-hardware-comparisoni intend to start a relatively slow rig, using a gpu i found on this website which has a fairly high khash/s-output/cost and working from there. i'm assuming the difficulty has gone up 10 fold over the last couple of days as the value of ltc went through the roof, so im not sure how well my card will perform (solo mining). but i feel it is the only way to gauge.
i am also in the fortunate position of needing a new graphics card, have a fairly decent second system i can pop it into, so if all else fails at least gaming looks good.
good luck
oh and you may buy at your own risk noone has a clue as to what will happen to ltc. $4.5 could be the limit.