score:3
From the first site you linked to, the key bit of information there is
OS 135 SH 663002
That tells you that you'll want to get hold of the Ordnance Survey Landranger Map 135 (Aberystwyth & Machynlleth) to cover you for the walk you'll be doing. The numbers are the grid reference, which tell you exactly where on the map you'll find the stone circle
Looking at the map, the stone circle is a few hundred meters over (but some distance higher!) than a very minor road. The road in question has National Cycle Route 82 going down it, so it should be pretty quiet.
Officially, it looks like you should be making us of the car park that is about 2.5km west along the road, at 642986. Looks like you can probably find some nice circle routes around there, maybe going a tiny bit further west along the valley, then up and finally east to the stone circle.
Alternately, there are a couple of farms just east of the stone circle on the road. You might get lucky and find that one of the farmers is happy for you to park there, but I wouldn't count on it. There's no way you'll be able to park on the road, it'll be much too small!
Update If you don't have the map to hand, this is the streetmap.co.uk view of the circle, and this is of the car park