Build a Low Cost OATS (Option 1)

With a $10k budget, you're close to being able to afford a full compliance OATS. Fully compliant OATS are usually constructed according to ANSI C63.7 (Guide for Construction of Open-AreaTest Sites for Performing Radiated Emission Measurements) and/or CISPR 16-1-4.

Your ability to construct an OATS on this budget will depend on the availability of a large open site with utilities and a building/cabin. You could set this up in a large indoor loading bay or on a rooftop, but keep in mind that you want to minimize reflections off nearby walls, cables and metallic objects.

Here's what you need to buy with your $10k:

Low cost spectrum analyzer ($1k - $5k)

At this price point, EMI receivers are not going to be within budget. I would look at a good, calibrated spectrum analyzer with frequency range 10 kHZ (so you can do conducted emission measurements too) up to 3 - 6 GHz. A few good options under $5k are the HP8560A, HP8563E and Agilent E4403B.

Buy them with a fresh calibration from a reputable cal lab (stickering without proper calibration is apparently rife).

One or two calibrated antennas ($500-$3k)

A good broadband EMC (hybrid) antenna will get you from 30 MHz - 2 GHz which will cover many applications. They're a combination of a biconical and logarithmic antennas which may be called hybrid, bi-log, bicon-log etc.. depending on the manufacturer.

If you want more accuracy, split this job up into 2 antennas and buy both a bi-conical and a logarithmic antenna.

Ground plane ($200 - $2500)

Your ground plane should be nice and flat and electrically contiguous (bonded at no more than every 1 inch). Chicken fence wire laid on top of flattened soil will be adequate in a pinch. A higher end solution is galvanized aluminum or steel with a minimum 16 gauge (otherwise welding gets very tricky and the plates bend in direct sunlight).

The size of this will depend on the antenna separation, but the smallest you would want to go is 8m x 10m. At smaller sizes, you'll have problems meeting the +/- 4 dB error budget.

Manual or automated mast ($500- $5,000)

For maximizing the emissions, you'll need to vary the mast height between 1 meter at 4 meters. The mast needs to be non-conductive. If you're on a tight budget you could make one yourself or look out for used one on ebay.

Manual or automated turntable ($10-$1k)

Again, for maximization, you need to be able to rotate the EUT 360 degrees. Ideally you'll have control of the turntable when you're standing next to the spectrum analyzer, so a motor controlled by remotely would be required. I bought a DC motor and variable speed controller from Ebay for under $500. If you're determined to cut costs, you can have someone else manually rotate the EUT.

Software for creating plots and including transducer data ($0-$2,000)

To be able to include the transducer data (the antenna gain, cable attenuation and possibly an amplifier), labs normally use automation software. You could do it manually in a spreadsheet, but it would get laborious and would be more open to human error.

There are a couple of good options here: KE5FX - a free toolkit that let's you grab data across GPIB ports. With a bit of programming you could set this up to rip the spectrum analyzer data into a spreadsheet.

Probably the best option at the moment, if your spectrum analyzer is supported, is the EMCWare software from Amplifier Research. It's free and looks to be really comprehensive for emissions and immunity automated testing (I haven't personally used it).

Finally, some spectrum analyzers let you input the transducer data manually and the readings on the screen are compensated.