Well for a 360 servo as I don't know of a single one you probably could just get an extremely high turn motor hooked to a ESC, and maybe connect it to a cheap transmission and use that. Or try and find a DC can opener motor. I had one many years ago I picked up at a electronics surplus shop for $5 it was geared very low, and would spin pretty nice at 9 volts that I used a few of them to make a robotic arm(which I sadly no longer got
as for the tilt servo depending on the weight of the cam you might want to get a very high torque servo.
Now I dunno what you are trying to make base wise but you could PROBABLY pick up a cheap Heng Long tank and just mount it to that as it will have the swivel due to the turret and all just would have to rig a pitch servo up
Only issue would be setting it up to run on a Dx6i but an australian company makes a conversion module for $45 or so so it can be hooked up to a normal radio(I dunno how good the part is I still gotta order one for my tank).
(only one they actually have in stock wonder how that place stays in business, or look to see if you can find the $69 tanks in stock somewhere I'd recommend the metal like I linked due to the tranny on the cheapies being kinda crappy though)
Dunno what your budget is cause budget build could refer to many things.