I have an ASUS motherboard with an Intel I7 processor. That gives me 8 vCPU's and I have 14Gb of RAM (could use more). I installed ESXi 5.1 on it with only the integrated NIC that wouldn't work. That wasn't an issue because I purchased an Intel 1000 Pro PT dual port server card off of eBay for $30. That is my vCD cluster. You can use just about any decent motherboard and processor. Stick with the AMD Opteron and Intel I7 or Xeon if you can afford it.
When it comes to building your own home lab you need to consider what you want to accomplish out of. Are you looking to mimic an enterprise environment to learn and what aspects? Are you looking to just horse around for fun??
I took an old dual core x64 PC and added 4 SATA drives in a RAID 5 config. Then I installed OpenFiler. Its a free Linux based OS that turns any PC into a iSCSI SAN. This is perfect for shared storage. Then You can get one (if not 2) cheap 1Gb switches (layer 3 if you can). This will allow you to create advanced networking, use vMotion, FT and iSCSI multipathing. You can get away with one switch but cannot multipath.
If you want a true cloud like infrastructure you should get another host for your "production cluster" as all the vCD servers and application should have its own dedicated vCloud Director Management Cluster.
If you really want to cheap it out and if this is for learning purposes, you could do this. Build or buy a PC with lots of RAM and CPU cores. Install ESXi, build a VM with ESXi on it (Yes, you can do that) then put your vCD server in that VM with ESXi and build out your vCD cluster, it will be slow but is a lab.
For cheap hardware that is know to work, check out the sites below. They are blogs where users have installed ESXi and said it worked because it won't be on the VMware HCL
Hope this helps..