When you buy a module... the Lugia Law of modular states you'll want to buy another one.
Starting out in a skiff means you're going to box yourself in in no time. There are tons of great modules out there but are exclusively in larger HP forms. If you put a couple of these larger beasts in your rack, you quickly run out of room. Having to slave your next purchase based on available HP puts a serious ding in your set-up when first starting out.
I think the Tip Top Mantis offers 208 HP (104HPx2) for around $300US. I would start in something like that. The balance between price and space seems about right.
I went with the Intellijel 7U 104 case (then bought another one). I still weigh the pros and cons of my decision... but I really wanted the 1U for attenuverters (Intellijel Quadrats). Inverting CV, mixing, etc... I paid the premium to have that.