Well we aren't far off the medical grade full genome for about $1,000. What I will say is that many tests that are available are 'low' for the exact reason that they need to be to attract people to them. Of course over time the cost of tests do come down.
But as a comparison I got my Y-Chromosome sequence couple of years ago for about $700, a number of other men in my genetic cluster did the same as a result it's possible to map out the shared mutations and branches in the lineage:
Black can be an angliscation for the same name in Irish that gave us Duffy (Ó Dubhthaigh eg. descendant of Dubhthach), of course what's interesting is that the three individuals with surname Black (Moore is case of surname change, ancestor was surnamed Black) all probably share a common ancestor in the early 18th century in North America, this ancestor had spilt from my own line probably during the middle ages, as a result they have a number of mutations that I don't carry.
Fisher (who has matched called Salmon -- both angliscations of Ó Bradáin potentially) in comparison spilt alot further back, probably during the early medieval period (5th-8th century), he shows up as a match for myself at only 67 STR's (not at either 37 or 111).
At the moment we are awaiting on another match bearing the surname Dowie (Dowey is a Donegal angliscation of Ó Dubhthaigh) to get his results, what's interesting about him is his parents were from Antrim (and Presbytrian to boot!). It will be interesting to see how he clusters as he's closer to them at 37,67,111 STR's than he is to myself.
To give another example, here is a tree built out of BigY results from men with origins in west of Ireland. The McManus family is historically noted as a branch of the O'Connor's of Connacht:
The four McManus kits on extreme left share a common ancestor who lived in colonial SE USA in the 1770's (he's down as a 'patriot') unsurprisingly they share 2 unique genetic markers not found in the next McManus kit. Some analysis actually puts the spilt between the two lines at about 600 years.
Stagpoole line is originally from west Galway (though surname is of Norman origin usually associated with Limerick). What's interesting about that kit is he shares at least two unique genetic markers with kit bearing the surname Connor (recent BigY not on that tree), they thus share a branch that is 'upstream' of the McManus men (eg. their lineage spilt first). All these inidividuals are close matches to a kit that belongs to a near relative of the current 'O'Conor Don'. The implication is that there is a good possibility that the DNA is actually backing up the historical genealogies when it comes to the branching of the McManus family from the O'Connor's during the 13th/14th century (they claim descent form Maghnus Ua Conchobhair d.1181). The current estimate is that the common ancestor of the McManus men with Stagpoole (and Connor individual) is about 1000 years ago
This hints that the Stagpoole individual might be a result of surname change at some stage (he has several other O'Connor matches as well as a McDermott match who haven't done advanced testing).
Of course getting people with deep lineages to do advance testing can provide an anchor line, so for example Baron Inchiquin (the 32nd great-grandson of Brian Boru) did BigY testing, his lineage thus provides a baseline for mutations among matching men bearing surname O'Brien (and other Dál gCais surnames)