I've aimed to get two of the "starter" armies... ie the oldest: High Elves, Orcs, Dwarves, Empire, Khemri undead, Chaos. ASAP - at about 50% RRP via ebay. Those armies you've chosen are the rare ones it's worth paying full whack for, except Undead, which seems to be the cheapest army to buy on ebay from my experience.
So perhaps skip the undead, unless you mean Vampire Counts. =-P
If I had to buy an army right now - would be Skaven - beautiful models!