I have 13 engines (12 O and 1 G) using battery power.
Your cheapest bet is to find an older engine in which the electronics no longer work (except the motor), in other words a shelf queen.
I have a Williams 4-6-2 and E7, a Weaver RS3 converted to use the BlueRail board.
I also have 5 Williams brass steamers, 3 MTH Railking steamers, and 1 Weaver steamer converted to use the Deltang UK/RCS Australia systems.
Finally I have a Bachmann G scale 4-6-0 Annie, using the Deltang/RCS system.
All run great, but I don't use smoke or (as of yet) sound, except in the Bachmann 4-6-0 Annie.
What I like about BPRC is there are NO WIRES to my layout. You can run multiple engines, separately, at the same time with BlueRail on a single device (Ipad), but you'll need a separate transmitter for the Deltang/RCS systems unless you want to run all the engines separately, otherwise they'll all respond to the single Tx. If you never plan on running more than 1 or a couple of engines that's no problem. I have 2 Txs for my O-scale layout and 1 Tx for my G-scale train. I usually run a train around the mainline while switching the industries.
Normally 2+ hours run time on a 2000Mah battery pack. I'm using 9.6v, 11.1v, and 12v packs.
I would guess the normal initial setup would run $175-$250 for a single engine, but once you get one the rest aren't as expensive, unless you buy a charger and Tx for each engine.
There's a number of topics and posts on BPRC, do a search and see what's happening. There's also a couple of online forums on battery powered trains.
