The Photography Plan, which includes the latest version of Photoshop and upgrades, as they become available, plus Lightroom, costs about £10 a month. The single app for InDesign is around £20 a month (you can pay a bit more and get it by the month, if you only use it occationally). The full Creative Suit is aound £50 a month. Students and teachers can get a cheaper educational rate.
Theoretically, if you are going to be using InDesign. Most likely you will also need to use Illustrator at some point. I know that you are looking for just Photoshop and InDesign. But my guess would be eventually you are going to need vector graphics and therefore would need Illustrator as well.
Of course, this really depends on what you are doing. But this is more of hunch and I am just thinking future forward. Raster graphics are great... and Photoshop will be necessary to edit photos for your layouts. But if you want to also add logos and other things then you need a vector program such as Illustrator as well.
Purchasing subscriptions à la carte costs more than purchasing bundles. It's that way with everything.
The basic Photography Plan bundle is just $10/month and you get a lot of great apps & online services for desktop and mobile. PS, LR, LR Classic, PS Camera, PS Express, PS for iPad, etc....
For an additional $20/month, you can add InDesign as an à la carte subscription. But I tend to agree with Ken. Eventually, you will kick yourself for not having Acrobat Pro, Scan, Adobe Sign, Illustrator and possibly Dreamweaver not to mention all the other great companion apps for mobile devices.
The last time I counted, The All Apps Plan bundle included 31+ apps & services. But nobody uses them all. And it's still cheaper than buying 3 à la carte subscriptions.