Budget Hotels in SFO near Union Square?

I am looking for suggestions for either budget or airline-discounted hotels in SFO near Union Square (walking distance)?

I am doing the Nike Women's (Half) Marathon in October and need a room that won't break the bank! Any suggestions?

I will be traveling with my husband, two kids, and mother-in-law - so we need a room with two double beds.

THANKS in advance for any advice!

-L

Try the Mark Twain. Few block from Union Square. Easy walking. Discount for Airline Industry. Stayed there for about $100.00

I haven't been able to find anything downtown cheaply but if you're cool with staying near the airport (SFO) and taking BART into the city, the Crowne Plaza, Red Roof Inn and La Quinta all offer airline discounts in the $45-65 (before taxes) range and provide hotel shuttle to airport where you can catch BART.