Welcome back to the hobby.. it is a good hobby to be in..
Things have advanced a lot though the basics remain the same.
Don't be scared off by todays high new prices as there are loads of secondhand bargains to be found.
Probably the largest difference is DCC, though one does not have to go down that route, as many of us just enjoy good old DC which is today considered the budget alternative. (It always worked for us in the past!

(DCC is a marvel, but can cost a fortune. Can also be frustrating in the programming side if one takes it to the extremes! BUT there are people here to ask if you go down that route and have questions so all is not lost!)
Depending where you last left off in the hobby, there are a lot more scales and gauges covered by the manufacturers these days. I have chosen 7mm scale narrow gauge as a budget friendly alternative to today's factory made models, though gradually factory made e items are now gradually entering this scale and gauge. (I still do my own thing and prefer making my own..).
Welcome back to the hobby!
Budget modelling in 0-16.5...