You never have to pay a cent. The game may still let new players believe that gear is locked behind a paywall but most items in the market have blueprints that you build by gathering materials in game and then waiting.
The things you can't buy blueprints for from the in game market are usually from clans which should be free to join (i.e., if someone is demanding you pay them for joining find a better clan) or earned in game during missions.
To be fair it has been a while since I was buying new weapons in the market because I am near level cap so I'm not sure how prominent the "Buy Blueprint" option is compared to the "spend premium currency" option but they did revise those screens to make it more apparent that real money doesn't need to change hands
That being said, if you wanna drop a few thousand I'm sure you can buy every available cosmetic, all the available weapons, all the available characters, the supporters packs, the prime access that's currently available, etc. I made my first purchase at like 500 hours and that was because I really felt they were improving the product better than some Triple A titles were at the time.
Stop by Dormi.zone to see what fans of the series are saying here on Lemmy. Afaik we aren't sanctioned by Digital Extremes but we haven't hit the critical mass of other websites yet so they don't see fit to pay developers to watch these boards.
Seconded. Let's not bring up playtimes and make anyone feel any sort of way but with over a decade of development, there will be something you can do. You can fish, you can hunt, you can ride a hoverboard, you can dance. Most of those things are just Open world things, but Warframe also has standard randomized tileset missions where premade tiles are laid out by way of some algorithm to make every mission unique while being built out of pieces you can become incredibly familiar with.
Beyond this, now that Cross Play and more importantly, cross save/progression is active you will have so many sweaty vets willing to help you on your platform (the Deck) and from other platforms like switch, PS4/5, and Xbone/Series.
If anyone feels interested in this game, definitely dip your toes and just take it slow. No need to rush things since you can always just take a break and try something else while things are building.