Can one write a research paper on a engineering project idea that one cannot execute due to financial constraints?
Yes, is the short answer, and in fact it happens all the time.
Go check out the journal Acta Astronautica for just one example - it is a journal about technologies and techniques for space exploration.  Many of the articles outline advanced space mission concepts and are done entirely in simulation, both because it is expensive (thus there is no budget to launch, say, 100 missions to Mars) and because an important part of engineering is the simulation and prediction of system performance.
However, there are other fields in which this is difficult, but not necessarily impossible.  It depends on the fidelity of your simulation.  A paper with a poorly made simulator that makes too many assumptions is likely to get rejected.
And this does bring me to a central part of this answer: you need SOME kind of results.  I spoke a lot about simulation, but there are other types of papers in which things like architectures or organizational plans are written about and (sometimes) accepted.  But ultimately, like the comments say, you can't just give an idea of what it would be like if you could do it.  That's the introduction to the paper, and it does not constitute a whole paper by any means.