As some have said, it really depends on how and what you collect.
You can be one of those ultra thrifty and patient people who only buy games for well under their going price. I've known people who refuse to spend more than $10 on any retro game and because of that they didn't accumulate games quickly or often. Also, collecting for certain consoles like the 2600 is now a very cheap endeavor as you can obtain 90% of the library for under $5 a game since it isn't a popular console to collect for anymore.
The opposite approach is to buy whatever you want, damn the cost. I've known very few collectors who take this approach since it can get extremely expensive, but some justify it by saying that they would just pay full price for a game versus spending countless hours trying to find it for cheaper. Their logic definitely makes sense since the time lost in game hunting is time that could be spent doing more productive or valuable things.
Personally I am about 80% the first time and 20% the latter type. Back when collecting and hunting for games on the cheap was a way more accessible and practical way of obtaining games I was almost firmly in the first group, as I'd feel bad if I spent more than $10 on a retro game, or essentially more than 1/3 of its going price. With finding quality titles for cheap being harder and harder, as well as finding what I still want being difficult due to its rarity and/or price, many games I have resulted to paying full price for or buying them when they are a decent price, but nothing crazy.
Another tactic I use and have used for a while is reselling games I have already or have no desire to own that I find for cheap in order to fund my collecting habit. The money stays within the hobby mostly and because of this I have been able to acquire many games that I wouldn't otherwise have been able to buy. I've known a few collectors who've even been able to pay for their collecting habit completely and then have some left over for other things. Given, these people generally watch CL all day long, have all kinds of ebay bot apps, and have turned hunting for games into a full time job, but that passion has resulted in them being able to create huge collections at no extra cost to them.