We have a Trek T100 Double Track (I don't think a Double Cross exists). It is something like '98 or '99, We have been happy with the bike for what it is. Frame is very good, components except for brakes have stood the test of time, and run well for what they are. Only repleced the original cantilever for V-brakes. However these are dated components, and upgrades such as changing the original flat bars for drops, or indexed shifting will likely not be worth the investment because the value of an older bike like this will not change with component upgrades and you get a cost cascading effect due to incompatibilities when you start mixing old and new which force you to change more than what you actually want to upgrade.
Price? I'd say $ 500-900 depending on the year and condition. Excellent bike in this range, very hard to find a decent tandem for under $1000. If the size is right, you are looking for a sub $ 1000 tandem, and you can live with flat bars and older componets buy it, you will not be disapointed. In a range of 1000-1500 you can find bikes which are more up to date.