A couple of suggestions on extenders.
Only do it if there is no option to wire in an access point.
If you can't wire in an access point, consider if you can run powerline adapters between the current AP/router and the location where you'd want the wireless coverage. If so, do that instead.
Finally if neither of those is an option, then look at an extender.
As for testing if it'll work at all, yes something like Netstumbler or InSSIDer can help determine this. Where you are planning on locating the extender, check the signal strength. I would say if you cannot get at least 70dBm signal strength at that location on EITHER band you plan on using as the connection back to the AP/router, then don't bother. It is likely so weak that you'll be "halving" a really crap connection. Now if all you need to do is get SOME KIND OF CONNECTION out to the new location and speed doesn't matter, you are probably fine down to around 80dBm, just be warned at levels above 70dBm, unless the extender has much beefier antennas than the device you are testing signal strength with, the wireless throughput is going to be attrocious and it'll kill (IE terrible throughput) whatever is connected to the original AP/router as well while something is connecting through the extender.
You can't really test at the location you desire to get wireless signal without putting the extender in, though within reason, you can test the signal from the original AP/router. If you can get signal most of the way to the new location before it drops completely, then having an extender part way likely will ensure some kind of signal gets to the final location, it just might not be a very good one.
Fast lane is likely not to be an option with what you are describing though.
What is the exact setup here? You mention a 9" thick concrete/block wall and 50ft, then another 50-150ft. Or is that seperate from what you were mentioning? It sounds like two different requirements for extenders? Multiple extenders is going to absolutely THRASH your wireless, even if you aren't extending an extender.
Other than the one wall, is this otherwise open space? Or minimal obstructions (cubicles)? If there are a number of walls between the extender and the 50-150ft...I would not expect the signal to carry. Maybe if there is one wall in the way that is not concrete, possibly. 5GHz and any obstructions and 150ft, almost deffinitely not.
What might be your best bet in both cases here are TWO access points to extend the signal. One access point in WDS bridge mode with directional antennas pointed back to the originating access point, then another access point with omnidirectional antennas plugged in to the AP that is in WDS bridge mode, with a seperate 2.4GHz/5GHz channel(s) set on it. That should give you a much better connection back to the originating access point and it also will not lead to a halving in throughput (because the basestation AP in operating on a seperate channel), though it'll still tie up wireless bandwidth from the originating AP.
