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A few options:
Buy and return at the store. Your camera shop buddies will probably understand if you bring back the lenses in perfect condition.
Rent. For my local store it's about $30-40 for 3 days for most lenses that cost around $1000, $50-60 for a week. Figure it out that way, then buy what you want. Personally I rented a Canon 24-70 and a 24-105 and decided on the 24-105 because of its cheaper price tag and IS.
Buy used, sell used. Used prices will be cheaper and you should be able to sell the lens for around the same price you spent minus a little bit ($50 or less in most cases. If you got a steal of a deal, you might even make money).
Also look at your brand's cheaper prime lenses. Canon has a 50mm f/1.8 for about $100, Nikon has a 35mm f/1.8 for $200 and are coming out with a 50mm f/1.8 for $200 soon. They're cheap enough to where you can just keep them even if you don't really use them often.