Both would have needed years of development and several billion € of investment to get to the flying prototype stage.
I think you may be wrong there. For one thing, the design that DASA proposed in 1995 was basically pretty much the same one that MBB had completed and nearly built eight years before, albeit with a few add ons (the idea now being less of a proof of concept and more along the lines of a developmental prototype). Another thing is that 4.5 million euros is around 8.8 million DM in 1981 money, the Euro having much less buying power than the old Deutsche Mark (not to mention that costs weren't quite out of control in the '80s as they are now generally these days). Not only that but that was the reported cost of the preliminary stage of the project, not the overall MRMF contract, which was never revealed if I am not mistaken. Additionally, West German R&D work on stealth aircraft in general had been ongoing since at least the mid-1970s. All this helps to explain how MBB was able to successfully flesh out a design for a flying demonstrator/testbed, which would have made heavy use of off the shelf avionics and other systems in much the same way that the US
Have Blue demonstrators did.
While the Lampyridae program undoubtedly had its domestic enemies (the, at times heated,
Deep Strike vs
Shallow Strike debate was still raging at that time, for example), the real foe turned out to be the United States. Unfortunately, when the USAF and DOD were informed about this program they had kittens. They were afraid that the ever efficient East German Stasi would be able to steal the plans of the MRMF and/or associated research and pass it on to the Soviet Union, potentially compromising the advantage that the United States had been able to gain in Stealth technology. More so, the US of course also dearly wanted to maintain a monopoly on stealth aircraft for as long as they could get away with it. Yet another likely factor was that during the late 1980s the US State Department was increasingly determined to try and shut down any advanced military aircraft programs in the West that could challenge allied procurement of US products such as the F-16 Falcon.
When DASA attempted to resurrect the program in the mid '90s, not only was the United States still hostile to any attempts to challenge its monopoly, but alongside the seeming lack of threat in the foreseeable future (classic End of History era shortsightedness) there was simply no money to be had for practically any military related programs, the defence budget having being rather dubiously gutted for the ostensible purpose of helping to cover reunification costs. The fact that with the end of the Cold War the anti-militarists were in the ascendance certainly didn't help matters one bit.