While buying bargain always seems the smart thing to do: Would you expect your Ferrari to still be under warranty if you took it to a cheap mom and pop shop for it's oil change and maintenance? I could give you the "support small business" morality talk, but it's more than that. I can not and will not guarantee a product you bought from somewhere else. You wouldn't buy a Samsung phone and expect Apple tech support would you? Sometime's it's not even a "superiority" thing so much as, "will this color technology work with that shampoo's version of "color safe technology".
If you have virgin hair, you don't HAVE to buy the nicest products, it is likely going to be healthy enough. Just like kids don't need expensive anti aging creams on their perfect angelic faces. So sure, there is absolutely a place for using budget shampoo and conditioner. However,its likely not the smart choice not if you are investing in coloring it.
If you were facing skin sensitivities or break outs, or you are trying to reverse aging, you've probably noticed that investing quite a bit more in higher quality ingredients for skin care is necessary for results. In fact if you are having extreme procedures like deep chemical peels done to your skin, it could have severe negative results if you did not use the prescribed skin care. The thing is, while skin is made of live cells that eventually rejuvenate themselves, hair is made of dead skin cells that once are past a point in damage- have to be cut off.
If you have long hair that has been on your head for 2-8 years, you brush it, curl it, flat iron it, and chemically process it with color or lightener, I would say the investment in the right salon products could actually save you money AND make your hair healthier and shiner.
How? A decent haircut probably costs anywhere from $50-150+. you might could be going longer without a trim if you used a good moisturizer and heat protectant ($20-$75) and your hair would look much shiner and have less frizz in between.
Is your color fading faster than you would like? Is your porous blonde turning a nasty yellow at the ends? It is possible that a good leave in conditioning treatment could help by keeping the ends from being overly porous. If it has a UV protectant that will keep your hair from fading as fast in the sun or yellowing (because if you can see by your patio furniture- the sun loves to fade and yellow things). This could save you money on toning in between appointments because a good leave in conditioner can cost anywhere from $20-75, and a toner or having to bleach bath the ends could be costing you $40-200 depending on how much hair you have and what you are getting done.
Your stylist is going to know what best to recommend based on what they use daily on their clients. Doing the same thing and expecting different results isn't going to help. If you absolutely love your bargain shampoo, that ok. Just don't expect your stylist to fix your color for free if it fades early.
A quality shampoo and conditioner are worth it to preserve the health of your hair, vibrancy of color, and help with styling. A leave in conditioner (spray, cream, or oil) can help you grow your hair much longer, prevent split ends, give more shine, and provide heat and uv protection, and help with frizz.