Be careful to make sure you know your needs they are removing support for IGC.
www.phoronix.com
Which may or may not matter to you. Additionally OS usage. Remember that past around 60 cores Windows hates it and if you go dual socket just make sure you read up on numa spanning and if such things will impact your workload, though admittedly, dual socket is more likely to get you the lanes you need cheaper then a newer build but still mobo prices are never going to settle. You arent going to find one anywhere close to consumer prices, for even the single socket systems with LGA sockets that large.
If you do try and cut costs in other ways, such as I mentioned before with ES/QS chips, be mindful if you are going intel to look at your chipset. The server boards with the server chipsets while compatible are more stringent in the micro codes they will accept and generally blacklist ES/QS samples. In rare cases you can find the qualification BIOS' but you will be running out dates stuff.
Depending on your workload also make sure that you are getting what you want out of the lanes. If possible check to see how many DMI lanes there are available to the chipset if you find yourself needing bandwidth from the chipset.