Take a look at these limited time fares from Southwest. One way mid-week fares anywere in US under $100! I've included the Las Vegas fare as an example:

Las Vegas, NV
$94 one-way, to/from Long Island/Islip, NY
$87 one-way, to/from Portland, OR

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IMPORTANT DETAILS
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*Available only on southwest.com.
*21-day advance purchase required.
*Available on published, scheduled service.
*Fares shown are one-way and do not include federal
excise tax of up to $3.00 for each flight segment.
(a segment is defined as a takeoff and landing) *Fares do not include airport-assessed passenger facility
charges (PFC) of up to $9 one-way.
*Fares are nonrefundable, but (except for tickets
purchased through our Group Tickets Program)
may be applied toward future travel on Southwest Airlines. *Travel February 5, 2002 through end of schedule,
except May 24, and 27, 2002.
*Purchase through January 17, 2002, midnight Pacific Time.
*Fares are available one-way or can be combined
with other fare types. Most restrictive rules of combined
fares will apply.
*Penalty applies to any changes made after purchasing
Southwest Internet Specials.

For more details, please visit us at: http://www.southwest.com/jp/hotfares2.shtml?src=e011502

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PROMOTIONAL FARE SPECIALS
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Promotional Fare Specials available for purchase January 15, 2002 through January 28, 2002!

SYSTEMWIDE - Travel for $39 to $99 each way on Tuesday, Wednesday,
and Saturday
*Travel January 22, 2002 through June 7, 2002.
*Purchase January 15, 2002 through January 28, 2002, midnight
Pacific Time.
*Fares are each way with roundtrip purchase.
*Fares do not include federal excise tax of up to $3.00 per
take off and landing.
*Fares do not include airport-assessed passenger facility
charges (PFC) of up to $18 roundtrip.

For more details, please visit us at:
http://www.southwest.com/hotfares/promotional.html#systemwide?src=e011502