as far as I know, the only steel frames you'll get under 4 lbs in 17" or larger are those made with True Temper S3 tubing, which True Temper recommends for "race day only" bikes. Too brittle to survive daily training or other regular use.
you'll have to contact a custom steel frame builder to get an S3 frame made. it's too chi-chi for regular non-custom frames.
I would expect to pay between 750-1500 USD for such a frame. the air-hardening process that makes such ultralight but relatively strong tubes will cause difficult metal work for the custom builder, so you won't find any real "bargain" frames in this weight range.
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