My condolences.

Time is an important factor with this. If the terms of the will mention it then greatest performance might be had from renting a dedicated machine in the short term. or purchasing might be better in the long term.

The former will involve more learning on your part however.

EDIT:
I have a little more time now to elaborate:

If we consider initial cost then a number of smaller cpu's running in independent rigs is cheapest but probably costs more to run than a single machine with more than one cpu fitted which would cost more to build.

The deciding factor will be the cost of electricity over the long term unless you live in an area of cheap electricity supply.

Purchasing and running any machine is the way to go if you intend to keep crunching WCG long term (lets say more than a year or 18 months)

If you think your plans are to do this for a shorter time then it would make more sense financially to investigate renting a dedicated server and learning how to set this up remotely. The same is true if you would like to make a large number of points quickly.

At this time WCG does not use graphics cards

My opinion, and it is just that, but spending $17k on hardware with plans to only run it for a year is not the most efficient way of doing it. Additionally, I don't know where you live, but here in Central North Carolina, where electricity is just under 10 cents/kWh, $500 a month would get you basically 7,000 Watts 24/7. That's a lot of electricity. I'm running a dozen and a half systems, mostly i7s, and my setup consumes under 3000 Watts (although I'm not sure how far under).

Personally, as hardware cost is the biggest concern for me, I have a motley collection of whatever was available at the time at a great price. This means my 24/7 fleet consists of four different generations of i7s, a couple older laptops, some Sandy Bridge i5s that I got scratch-and-dent, a 32-core AMD Opteron system, and a recently-build Westmere dual-socket system. However, I would suggest that you go with something more uniform--a collection of identical Haswell i7s or AMD FX8 systems would be a straightforward route to go, or you could opt for multi-CPU systems instead.

Lol. My electricity cost for my whole house is about $11 per month and this includes running two WCG devices (a G1610 and a Tegra Note 7) for about 10 hours per day each. My kwh cost is about $0.27 in the UK.

Sorry for your loss. I suggest a dual processor system. 12 core or higher per processor. Make sure you include a nice UPS to protect it too.

Firstly, very sorry for your loss!

Secondly, it might be worth having a look at the new LGA2011-v3 Xeon chips, they now go up to 14-core (28-thread), and don't seem to be ridiculously expensive. Not sure how they compare, performance-wise, with the older LGA2011 chips (someone else may be able to answer that), but I'd say they're worth considering.