You can step in a different direction by having a small value-added reseller (VAR) build the nodes for you. The obvious advantage is that a VAR has to support the node when it breaks. But if you buy your boxes online (as opposed to locally), you'll likely have to ship defective units back to the VAR for repairs. You're also stuck with whatever hardware the VAR offers, while specifying your own configurations may drive up the price if you start asking for components that it doesn't stock.
Many places will also start looking at you strangely when you ask for these types of configurations because they have no experience with people wanting to build their own render farms. When VARs do build systems like this, they usually expect to put some type of server operating system on the machine. If you don’t specify otherwise, they might think you're talking about some type of low-spec file or transaction server. However, once you explain to them what you need, most places should be able to build the nodes fairly close to the same specs as if you were building them yourself, but at a slightly higher price. Then, once you receive the node, you have to install all of your applications to each system separately or invest in management tools that allow you to do bulk installs.
If you get a VAR to build your nodes for you, you’ve opened up several new possibilities. One “put-all-your-eggs-in-one-basket” option might involve a single 1U enclosure like the Supermicro SuperServer 6015T, which has two dual-socket Xeon LGA 771-based processors in a 1U rack unit, meaning you can put 16 3.2 GHz processor cores in a single 1U enclosure. Of course, this unit also has a 980 W power supply and, at its peak power load, its power requirement is similar to that of 10 1U nodes.
If you need a lot of processor power in a very small space, a few Supermicro systems might be a good idea, especially if you are running a virtual studio where you have access to better power circuitry and ventilation designed to handle this kind of setup. These Supermicro high-density systems are going to get very warm.
Another option is investing in ATXBlade units. ATXBlades are like the blade servers you may have seen, but they use commodity ATX motherboards and can be configured like a normal system. Additionally, they allow you to fit 10 nodes into 8U worth of space. However, ATXBlades only accommodate a limited range of motherboard products and other components. Still, you can get the ATXBlade chassis and blade units with motherboards and no other components, and then you can build the nodes yourself. In discussing these, we've kind of diverged from a home-freelancer setup into a small-studio discussion because the setups we're talking about are getting progressively more expensive, and also are consuming more power and generating more heat. An ATXBlade unit consumes 2,000 W at 100% CPU and I/O utilization, which is more power than is available on an average single-household circuit, making this an option for a small boutique studio.
Buying From a Tier-One Vendor
"Buying commercial" involves going to a so-called big-box vendor for your render nodes. The big advantage to this option is that a large vendor is going to have a well-trained support staff if you're a business customer. Both Dell and HP have departments that are experienced in supporting 3D animation, editing, and compositing software if you are a business (and not a home) customer. Business support also means you can get someone on the phone 24/7, and in most cases if you spend the money, you can get next business-day (or even next-day) on-site repairs.
There are also specialist vendors like Boxx Technologies, which has been building workstations and dedicated render nodes for the industry since 1998. Boxx’s advantage is that its machines are designed from the ground up for this usage model. Its renderBOXX module puts two dual-processor, quad-core systems in a single chassis, which is designed to be racked with other modules. Boxx also supports pre-installation of applications and render controllers on the modules. Five of these units (80 processor cores) will fit in a 4U rack space. But each of these modules has two 520 W power supplies, translating into a max of 1,040 W per unit. Specified power consumption at 100% duty cycle is 414 W per unit with two Xeon 5580 130 W processors, but most of Boxx's systems are shipped with less-powerful CPUs. The caveat is that these systems start at around $5,000 per module, or about $25,000 for a full 80-core unit.
Most business-oriented vendors would essentially sell you low-end 1U servers molded into a custom configuration to meet your needs for a render farm. Examples of these systems would include the HP ProLiant DL120 and 320 series or the Dell PowerEdge R200, once configured with appropriate memory and operating systems. The serious high-density computing setups from these vendors become outrageously expensive and are completely over-spec'd compared to what anyone except the largest studios would need for a render farm. These systems also are designed for a server room installation and are really not meant to be deployed in a home. While having a monolithic rack of high-end blades in the corner of your home office might look impressive, the $45,000+ price tag is a lot less savory.