I have a sum stored away in a US bank and may be interested in doing a cash purchase of a small site.
Would i have to transfer the money to an irish account first?
Or could i arrange to just do a transfer from US bank to the sellers Irish bank?
The charges and FX rate will most likely be the same if you are transferring to your own Irish account or the seller's. Depending on the sum to transfer you may be above the maximum allowable amount so may need to do a transfer in multiple smaller blocks, each with their own charges.
The Irish bank (and possibly also the solicitor too) may need proof that the funds originating in the US stem from legitimate activity. This is to comply with anti-money laundering legislation.
It's good to have this proof to hand in case you get asked for it as otherwise it could slow down the process.