we want 6-8dbi omni antenna design solutions for low profile very
compaq and less price for frequnecy range 800-900 Mhz

The lower the frequency range, the larger the antenna would need to be
for a given amount of gain. For example, I have a 2.4ghz omni antenna
with 9dbi gain which is 2-3 feet long. A 6-8dbi omni antenna operating
in the much lower frequency range of 800-900mhz would likely be much
larger as a matter of physical properties of commonly used antenna
designs. It may be possible to make a compact antenna that does not
radiate omni-directionally with that gain, but any omni antenna in
that gain at that frequency could not be described as "compact"