Thanks for the info.
Abt budget, this will be only the second time I'm actually buying a case and first one was with PSU. Without any history or knowing what features make a PSU good/bad, it's really difficult. But let me add that the budget for the NAS itself is around 6-800. I'm planning to reduce the number of HDDs from build if I hit the limit, it's RAID (RA of "Inexpensive" D) after all and I'll add more later.
What I can say for sure is I won't be adding any graphics card anytime soon.
If you really push me for a number: Looking at the list on newegg for 401-450W PSUs (http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007657%20600014019&IsNodeId=1&bop=And&ShowDeactivatedMark=False&Order=RATING&PageSize=100),
I would say perhaps $40-60, viz around median, should be enough.