We need to know what the average percentage of a consumers average
salary is spent buying sales taxable items.  Also, is there a
significant change in that Avg. in relation to the size of the income.
 We need to be able to site the source of the information, and have
confidence that the source is credible.  This figure is needed for an
informational campaign on a local ballot issue.  example: Just how
much will 1/4 of 1% sales tax end up costing Joe Consumer at the end
of the year.  If regionalism is a factor, we are in the middle of
Missouri.

I believe I've found precisely the kind of figures that you need in a
recent document published by the Institute on Taxation and Economic
Policy. I've discussed a few excepts below, but you may want to read
the document in its entirety.

According to a chart that appears on page 3 of the document,
Missourians in the quintile of the population with the lowest income
(averaging $8,900 a year) pay 4.1% of their incomes to general sales
taxes (these are sales taxes on individuals rather than on
businesses). However, the richest 1% of the Missouri population (whose
incomes average $689,000 a year) pay only 0.7% (seven-tenths of a
percent) of their incomes to general sales taxes. So, proportionally
speaking in relation to income, the sales tax burden on the poor is
nearly six times that of the very rich.

Institute on Taxation and Economic Policy:
Missouri Taxes Hit Poor & Middle Class Harder than the Wealthy
http://www.itepnet.org/wp2000/mo%20pr.pdf

The document linked above is a portion of a nationwide study:

"Who Pays? is a comprehensive analysis of state and local tax burdens
in all fifty states. The study, released on January 7, 2003, shows
that on average, state and local tax systems require the poorest
taxpayers to pay the highest effective tax rates."

Institute on Taxation and Economic Policy: Who Pays?
http://www.itepnet.org/whopays.htm

This article, from "Citizens for Tax Justice," utilizes the ITEP
study, among other sources, in making suggestions for tax reform in
Missouri:

Citizens for Tax Justice: Revenue-Raising Options for Missouri
http://www.ctj.org/pdf/mo0403an.pdf

Here's good another article. This is specifically about sales tax
issues in Oregon, but I believe you will find useful material here:

Oregon Center for Public Policy
http://www.ocpp.org/2003/issue030707.pdf

These were the Google search strings that brought me the best results:

Google Web Search: "sales tax" poor OR "low income" missouri
://www.google.com/search?hl=en&ie=UTF-8&q=%22sales+tax%22+poor+OR+%22low+income%22+missouri

Google Web Search: "sales tax" regressive poor income
://www.google.com/search?hl=en&ie=UTF-8&q=%22sales+tax%22+regressive+poor+income

I hope this helps! If anything is unclear, or if a link doesn't work
for you, please request clarification; I'll be glad to offer further
assistance before you rate my answer.

Best wishes,
pinkfreud

Sorry for the delay but I thought the real test for this answer was to
see how the comittee felt about it.  They seemed to agree that the
sources legit and the numbers we have been wondering about for 6
months were all there.  The speed of your answer was pretty impressive
too.  Thank you

Thank you very much for the five-star rating and the nice tip. I am
glad to have been able to help, since I believe that sales tax reform
is an important issue. I wish your committee the best of luck!

~pinkfreud