The New Construction (Single Family) permits range from $100,000 to $705,000, with an average of $243,255.

Ada County Permits 1/1/2010 - 11/15/2010
Description	Count	Average    Permit	Total   Permits
New Construction	126	$243,255	$30,650,102
Addition	61	$42,572	$2,596,921
Detached Accessory Structure	55	$29,624	$1,629,342
Remodel	18	$31,169	$561,036
Pool	11	$36,000	$396,000
Firebird Raceway Tower	1	$370,846	$370,846
Fire Damage	8	$30,597	$244,777
Covered Patio	26	$6,744	$175,332
Cell Tower	7	$17,857	$125,000
Office	1	$82,000	$82,000
Sign	3	$25,530	$76,591
Public Restroom	1	$60,000	$60,000
Deck	9	$6,067	$54,602
Water Tank	1	$50,000	$50,000
Roof	2	$19,462	$38,923
Scales	2	$16,750	$33,500
Shop	2	$14,500	$29,000
Oregon Trail Interpretive Kiosk	1	$20,000	$20,000
Misc	23	$718	$16,509
Wall - Sewage Lift	1	$12,975	$12,975
Fireplace	29	$345	$10,000
Monuments	1	$8,000	$8,000
Personal Property	8	$625	$5,000
Antenna	9	$444	$4,000
Gas Piping	51	$1	$67
HVAC	1	$0	$0
Vent Systems	6	$0	$0
Water Heater	17	$0	$0
Furnace	225	$0	$0
Compressor	29	$0	$0
Demolition	6	$0	$0
Grand Total	741	$50,271	$37,250,523

The data was taken from http://www.adaweb.net/DevelopmentServices/BuildingDivision/CurrentPermitInformation.aspx and analyzed.  I took the liberty of removing the 32 double permits (same permit listed twice) and adding basic Description heading to better understand the 741 permits.