The majority of that is true of any hobby or passtime over the coming years. Everything is getting more expensive.
People starting off shooting will still be able to use airguns.
People starting off will still be able to buy cheap shotguns capable of shooting SP steel. Steel cartridges are no more expensive than lead.
People starting off will still be able to buy cheap full bore rifles and there is affordable non-lead ammo that works.
I am already doing all of the above and I'm not in any way well off.
steel cartridges with biodegradable wads are more expensive than lead with fibre wads, you need to compare like with like.
The issue then becomes is it acceptable given the worldwide focus on plastic pollution for shooting to claim its green when scattering millions and millions of single use plastic wads around the countryside. Which as I said previously is now the problem Denmark is facing.
Personally I have no problem moving to steel, however I too am not any way well off, so my current thinking is to buy as you say a cheap shotgun and use steel shot with standard fibre wads, if I have to buy a new gun every few years it may well be cheaper than buying several thousand cartridges with biodegradable wads over the years.
wads by the way that for some take a few years to degrade and one farm I shoot over has already said they do not want them used. As when I did try some they were on the grass fields like four bladed helicopters and it is a dairy farm, their business, their cows, their land their rules or shoot else where.