This article is assuming you have a limited budget and you want a budget guide to build a deck and get the best value out of it. If someone can afford the budgetless options, that’s fine and there is still reason to continue reading as spending more money doesn’t always get you the optimal choice (but it is true that since the prices reflect the market supply and demand, the most sought-after cards are usually the generic best ones).
But what if I told you that there can be slightly worse, equal or even better choices for about 10% to 1% of the cost? You might wonder if that is even possible. The trick here is that the most sought-after cards are usually the generic best ones. Meaning they are the best overall cards for most of the decks and that is raising their demand. But sometimes there are specific cards (that work only on a very specific deck/strategy) that can do almost the same job for way less money since the demand for them is significantly lower as they only work great on a few decks/strategies and are strictly worse to terrible to most of the other decks/strategies. The more specific the card, the cheaper its price is. Let’s get to some examples.
Counterspells
Budgetless option:
(cheapest ~40$ but can get to 60-80$ depending on versions and availability)
For 
you counter target spell and it ramps you ahead of your opponents on the following turn. It is as overpowered as it sounds.
Generic staple:
(cheapest ~2$)
For you counter target spell. Strictly worse than Mana drain but still it gets the job done for ~5% of the cost. It is the main counter staple.
Specific budget option example 1:
(cheapest ~0.2$)
For 
you counter target spell and scry 1. In most decks it is worse to slightly worse than Counterspell. But for example in a specific deck that care about scry (like one with Elminster as commander) due to synergy it is an equal to better alternative to Counterspell for ~10% of its cost (and 0.05% of the Mana drain cost).
Specific budget option example 2:
(cheapest ~0.2$)
For you counter target spell and both you and the owner of the countered spell draw a card. For most decks this is a kinda worse counterspell, but for specific decks that care much about draw and opponents draw like wheel strategy decks, it can work wonders as synergy makes it a better alternative to Counterspell for ~10% of its cost (and 0.05% of the Mana drain cost).
Specific budget option example 3:
(cheapest ~0.2$)
For it is a strictly worse Counterspell as it needs a specific situation (costs less to cast if you control a Wizard) to just become equal to it. But even if in 99% of the decks this is worse or too situational, in a wizard tribal deck where you control a wizard most of the time, this becomes nearly equal to Counterspell, while being 10x cheaper.
Mana Drain remains better at most cases but even the fact that cards that cost 0.2$ can be better alternatives to a card that cost 10x more and even compare to a card that costs 200x more is insane.
Some thoughts on deckbuilding diversity: Although some budgetless options are quite hard to be outmatched by budget alternatives, as a deck builder, I find that those cards hurt building diversity as they are the optimal choice for every deck and in a way, there are 10-20 cards that they could be part of every single deck out there, so including lands, more than 50% of every deck could be similar and lead to repetitive games. I’m not against using cards like Mana drain (I wish I had one in my collection) but if I had one I’d prefer to use it on a deck that could maximize it’s efficiency (like a deck with high need of colorless ramp) rather than make proxies of it and use it on every single deck I have that uses any kind of counterspell.
The use of proxies is another factor than can hurt diversity as it leads you more and more to use the same cards rather that finding (cheaper or better) alternatives, but still I’m open to discussing their use in games I play as long as it is fun for everyone.
