Need WordPress plugin for automatic custom field values – autoblog

Based in “autoblogging wprobot system I already use”, I would like to have automatic custom field and values created for 2 kinds of themes.
You may know some themes, like classipress, need custom fields filled to work great, like showing price, location, etc.
This happens cause those theme, as others similars, requires some custom fields and values to be created.

JOB:
1- Auto create custom fields variables (will be always the same for each theme, like: price, location, number of bedrooms, etc). “easy”
2- Harder step would be auto getting and setting values for each custom field, acording to post content.
Sample: My feed source code will have “the price value” between a html command, like <!–price–> VALUE <!–/price–>
Idea would be telling the plugin to catch values inside each html code, pre-determined.
Remeber that I can have feed with other htmls for cathing other values for different custom fields, like colour of the car, num. of bedrooms, etc.

*THIS plugin got to work in any theme, since just need custom field variables and values to be catched based in html post content commands.
So should work also in:

PS: In numeric custom field, I would need (somehow) to also make maths equations, like:
function: (get price value) ADD 15% or add 5 or subtrct 10, etc.

That’s all.
Doubt’s? Need to know rss feed sample and admin log’s?
Let me know.
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Can do it?
Tell me:
1- Price.
2- How long will take.
3- Pay method.