While it seems this subject has largely been discussed thoroughly, I will put out a vote for Pentax digital. I have shot 4x5, medium format, and a large variety of vintage cameras over the years, but my very first "pro" quality camera was the Pentax K1000. I still have it and carry it on back country trips as a back up.
What I like about the Pentax system is the amount of features versus the lower relative cost for equal quality products. I have progressed from the K1000 through the ME Super and Super Program in film and then into the *istD, K10D, K5 and just now the K1 full frame 35mp. While I have newer lenses all my old ones are compatible with every K-mount Pentax ever made without an adapter. That means that my 1970's vintage 50mm / F1.2 lens and 20mm / F4 lens are still useful as they still cost about $350.00 each on the secondary market.
Lately my main lens for railroad photography is a Sigma 135-400mm zoom that has given me consistent results on trains. I also like a wide-normal zoom lens.
Regardless of the system you go with, remember that when purchasing a DSLR you are buying into a system, not just a camera. To keep in your budget any of the major brands with the kit 18-55mm lens will be a great start. You can expand the system as funds permit. The biggest thing is to try them all and decide which one feels best in your hand.
For me, staying with my original brand of camera loyally for 30 years has meant that I have an incredibly diverse collection of gear that all works within the system. The camera is ultimately a throw away anymore which is the big change from the film era. You are really investing in lenses that will hopefully give your many, many years of quality service. As an example my APX sensor digital bodies, the Pentax DA 16-45mm has been in use for 13 years during which I used it on three separate bodies.
A variety of photos all shot with my Pentax Digital gear. Only three lenses were used on these; 16-45mm Pentax, Sigma 10-20mm, and Sigma 135-400mm.
One thing about us Pentax users is that we are so fiercely loyal to our brand we are known at "Pentaxians". Depending on who you talk to, it's a badge of honor, or a slur. 
Arizona Eastern Railway Excursion Train in 2011, the last year it ran before the line was sold by SLRG to the Genesee & Wyoming and the service stopped: Pentax K10D with Pentax DA 16-45mm.
UP 844 when it visited Arizona in 2011: Pentax K5 with Sigma 135-400mm.
30th Street Station in 2012: Pentax K5 with the 16-45mm lens
Then New GE ET44AC's in February of 2016 on a cloudy day in New Mexico: Pentax K5 and 135-400mm lens.
Amtrak fun under wires during my York trip last April: Pentax K5 with both 135-400mm lens and the Sigma 10-20mm lens. To be honest, I haven't been extremely pleased with the 10-20mm. It tends to be fuzzy at the edges. I just had to learn how to shoot with it and how not to shoot with it.
Railroad Museum of Pennsylvania in 2008: Pentax *istD with 16-45mm lens.
