Are you looking specifically for new copies? Because CEX has them relatively cheap (I know they can be a shitshow though). Besides, El Shaddai is not on the service, so you'd better check any other titles that you want for availability.
As I have a US PSN account, I actually did find El Shaddai on PS Now.
Playing the long game with eBay will probably be your best option then. Keep an eye on listings for long enough and you're bound to run across a copy that is cheaper than average.
Also, this is probably the best time to buy games for that generation. We're in that part of the cycle where there are a lot of games out there for good prices from people offloading their collections from last-gen, but before the kids that grew up playing those games get bitten by the nostalgia bug and have the income to feed into it, causing the prices to start shooting up.
It sucks that we have 3 similar services to eBay/amazon in my country (Romania) but rare, obscure games that I like can't be found ever. That was my best option to find them pretty cheap, and I've been playing the waiting game for years but to no success.
I wanted something intermezzo before the big boys I've mentioned launch, and with the eBay delivery times, prices and hooking everything up just seems too much at the moment for my limited free time.
I guess I'll bite for one month PS Now sub and see how that goes as my internet is pretty ace.