ok...here is the picture
http://cakecentral.com/gallery/1937842
How many servings will she need?
Can you just biuld a block of wood from scrap wood to elevate the entire cake or ask her fiancee to do it? Just spray paint it brown/cream, cut out some horseshoes, bandanas etc from Scrapbooking paper and glue on the outside of the "stand"
This is so silly of an answer but at the Western Wear shop here they have a gift section of western items. They have some unique ideas that might work, some as is or with just a little modification. They were reasonable priced and would be less stress than trying to fabricate something. Good Luck!
You could do a seperator wrapped in rope...
Or covered in fondant and make it look like leather. That would be really cute with that style of cake!! I would do it in the dark brown color then just put leather designs on it.
Or wrap it in a brown or cream colored bandana...
Or making it look like a fence post is a good idea too...
I'll let you know if I can think of anything else!! (I live this style... in the Texas panhandle... 
)
Quite honestly though, her budget problems are not yours.
Either she setlles for a smaller cake, enough to feed the people she has invited, scale down the entire party to accomodate her budget or she can make her own separator, so that the cake looks larger (or buy, if she has the money)
Even if you have to make one or buy one, it's your time and money, which she has to pay for.
I make nearly all of my own party decorations (in addition to the cake), because a.) it's fun, b.) it's cheaper and 3.) I can hardly find anything here to fit my crazy themes and ideas.
What about using a slice of wood from a log that still has all the bark on it for the cake stand? That would give you some height. You could even burn their initial or intials into the bark or make a small plaque with the monogram on it and trim the plaque with rope and attach it to the bark stand.
For separators, you could use the regular grecian columns and make cowboy boots or cowboy hats to go around them.
What about using a slice of wood from a log that still has all the bark on it for the cake stand? That would give you some height. You could even burn their initial or intials into the bark or make a small plaque with the monogram on it and trim the plaque with rope and attach it to the bark stand.
For separators, you could use the regular grecian columns and make cowboy boots or cowboy hats to go around them.
I like this idea
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