Brulo's shop

Hi folks! So i got a question about brulo's shop and i simply need to have things clarified

When i first started playing the game , after beating boiler city i bought the canisters and left the cassette and the tv alone thinking i could just buy them after beating the second level ; But to my surprise , turns out they changed for new stuff along with new canisters and realised that these items don't stay in place and have to buy them BEFORE progressing through the game...or so i thought.

So i just thought "fair enough" , proceeded to delete my save and start a new one with the goal to NOT progress and instead grind currency through boiler city and saw that there were additional game modes and thought to myself "oh maybe this is intentionally designed so you have to fully complete a level to give you enough money to buy the collectibles presented the first time" , but then when i beat the time trial and revisited the shop THE COLLECTIBLES STILL CHANGED!!

SO WHAT GIVES ?

Are you supposed to just get the EXACT amount of money needed the first time otherwise the collectibles are just gone forever or do they simply cycle through until they return back to the first set ?