According to the January '06 issue of Smart Computing magazine, in which they reviewed four such products, including the recent version of FileMaker Pro, Your best bet may be the best deal, as well.
Here are the homepages for each product and it's price and the score the magazine gave it...
Database Professional 1.5 - $50 - 4.2 out of 6
http://www.shop.avanquest.com/usa/prod.php?pid=68
FileMaker Pro 8 - $300 - 4 out of 6
http://www.filemaker.com/products/fmp/
Alpha Five 7 - $350 - 3.7 out of 6
http://www.alphasoftware.com/
Microsoft Access 2003 - $230 - 3.7 out of 6
http://www.microsoft.com/office/acce...o/default.mspx
According to the article, Database Pro was given the highest score based on it's price and ease of use. Both Alpha Five and Access offer a few more bells and whistles, but your client will have to compare them to see if the extra cost is worth it. Also, the $50 for Database Pro is for two computers. Additional licences are about $20 each, so that has to be taken into consideration.