If "cheap, immediate" replacement is truly the issue, a small used Corolla (gas/manual tranny) may be what you need. You pay a premium for the extra technology in either the Prius or TDi that could take years to recoup through fuel savings alone. Used Toyota gassers should be plentiful and reliable even if they give up a little in ultimate fuel economy.
If you want fuel economy and performance too, get the TDi.
