If I can see the coin in hand before I buy, or if I'm buying it raw from an auction house I trust that has a good return policy, then I don't have any particular limit. If I'm buying it raw on eBay or the like, then it depends entirely on the quality of the pictures and the seller's return policy. One time I paid just over $700 for a raw eBay purchase, but that was a true outlier - the coin straight graded and is one of my absolute favorites in my collection. Typically my max for a raw coin on eBay is around $450, and that's from a good seller with good pics.
I paid $1200 for an au 1955 double die wheat cent. Sent it in for grading and came back as counterfeit. I was able to get my money back and dealer paid fee for the grading.
News flash, 'dude: The title "novice collector" under your username is not really applicable in your case, at least not any longer.... I'm still novicely learning. 'dude
When my collection was primarily raw coins I would spend $400 for silver and up to double the melt value for gold - if I liked the coin. Once I decided to grade all of my coins I stopped spending that much on anything that wasn't already graded. All but one of the coins I owned at the time and were worth submitting for grading got clean grades (I didn't bother with the lower cost coins - I just sold them raw). I had good luck I guess.