It depends on what you are understanding about "cheap" 
The problem with "cheap" laptops is that you have slow 5400k harddrives, which realy sucks and it´s fun at all to play around which a hole environemt storing on one single 5400k drive. Of course a SSD drive would bring you to a hole different level, but its also much more expensive.
I am currently using a laptop for my VCP5 prep. I am having a Fujitsu NH751 with a i7-2630QM, 8GB RAM, 90GB SSD & 750GB HDD which costs around 1100€ in this configuration.
Even with this 8GB I am getting fast to the limit. You need to have 2GB for each ESXi (which will be the minimum for testing vMotion etc.) and you need to have a vCenter. I used the Linux Appliance of vCenter an this one is allready swaping if u are using just 4GB RAM.
Not to forget: The Win7 of the Notebook also needs not less of the 8GB, because usually during testing with vSphere you have open your webbrowser, pdfs etc.
I am thinking acctually to update the 8GB to 16GB, but 8GB Modules are like the SSD not cheap.
If you want to save money you are much cheaper if you are taking a workstation build with an Intel i5, 16GB and some more SATA disks (maybe in Raid). I guess this will cost you max. of the have of a laptop and still will have more performance because of more RAM and multiple disks.
To use a shared storage i recommend you to share a vmdk file between multiple ESXi. So you dont waste additional ~1GB RAM for a SAN Appliance.
Cheers,
Mario