If the Blackburn is your dream horn, by all means get it. But be prepared - your dream horn may become a nightmare.
I'll just tell a few tales from my experience.
Many years back, a corno da caccia was my dream horn. And then, during a historians' conference in Leipzig, I stumbled upon Friedbert Syhre's workshop, and he had one just finished and ready for sale. Silver plated, with gold accents. I talked to my bank manager on the phone for about three hours, and bought it five minutes before the shop closed for the weekend, for something like $ 3,500. I had found my dream horn!
And then I slowly realized I would not be able to use it much. I was not good enough at that time to play the original music written for the corno da caccia, and there were literally no chances at all to use it in orchestra. I played it once or twice in local church orchestras, doubling for French horn. But for more than nine years, it lived a very quiet, secluded life in its case.
Until someone really needed one to replace one stolen during a rehearsal, and I sold it on for less than $ 1,000, just to have it played.
Then, for many years, a Scherzer G picc was my dream horn. I saved all I could for about five years to be able to get a new one, finally bought one; nice horn, loved the sound... found an orchestra that wanted me as a soloist for the Torelli concert and as an orchestral principal trumpet for the Haendelujah (me with the Scherzer) 
, and I practised like mad, only to overdo things and lapse into pneumonia two weeks before the planned concert... had to take time off to recuperate, by which time the concert had been played by a sub. I used it for some more time, sparingly, until one day, after a playing break of about two weeks, I took it out of its case and the valves were frozen and I could not do anything with them, had to get them repaired and had that reoccur several times. And when Maurice André's will left me a Selmer high-G and I found that easier to play, it went its way to a new owner.
Two or three years after getting the Scherzer, I had acquired a Besson Kanstul 920 picc. Wonderful instrument, and they tell me I sounded really good on it. No problems - except that I had set my mind on a Stomvi. So I sold the Besson in part-exchange. The Stomvi was nice, no doubt about it; but somehow, it was not the instrument for me. I needed much more lip pressure than with the BessonK, put too much hand pressure on the valve cluster and thus got the valves to stick... !
Pic shows me with the BessonK.
I can tell stories like this about many of my dream horns. All of the horns I play now are horns that happened upon me somehow, without me really planning to get them, like my Courtois 154R flugel which I acquired at a trade fair when the Courtois people had a few instruments left over which they did not want to take back with them; so my advice is, don't search for a specific horn, but look around for anything that drifts your way; try, try and try again, and at some time, your dream horn will find you.
