>The only disadvantage that I can see to using SQL-server, Oracle, DB2, etc. is the cost. Suppose I try to market the reservation app that I have written. Most resorts that would use it would have between 10 to 30 workstations. Say I sell the app for $1000 per workstation most of which is profit. (Not necessarily the way I would market it but close enough for discussion.) If I put the data in a SQL DB my cost goes up by about $250 per workstation, significantly reducing the profit.
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>How have you dealt with this?

If you're concerned about up-front RDBMS costs, keep an eye open on Linux developments. I understand that there is now a decent free back-end available, PostGRES SQL, and a Windows ODBC driver is available.

Of course, there's no free lunch here, Linux configuration and management costs are going to be scarce and more expensive in the short term. I'd look closely at upcoming Linux-based "appliance" servers that could easily have a back end installed on them.

If you went this route, theoretically you could spend some time optimizing a standard Linux installation plus your backend setup, then "ghost" the hard drive to create a new backend box for a new client. Wow, no software licence fees - what a concept!