Ultimate Masters is the last Modern Masters set in the "foreseeable future" according to Wizards of the Coast. Without new MM sets, Modern staples are likely not going to be reprinted as frequently as they have been. As one of the most popular formats in MTG, prices on Modern staples have continued to rise as more people jump into this eternal format.
The best part about Modern is that once you buy-in, you are set for life (unless of course your deck gets banned). If you are looking to get into modern, or want to get staples, you better do it soon! It's probably not going to get cheaper anytime in the "foreseeable future".
Here are 12 Magic: The Gathering Modern Staples You Should Buy Before They Go up in Value:
Last year, Ancestral Vision was valued at $40 before it was reprinted in Iconic Masters. Ancestral is such a powerful card. Nothing can really match its raw draw potential at one blue mana in Modern. At around $10, I don't see Ancestral Vision going down anytime soon.
Voice is another $40 card that has slowly declined in value over the past few years. It's only been printed twice, and at mythic rarity each time. The price has been pretty stable at about $10 for the past year. If control decks get popular again, decks that utilize Voice of Resurgence may become more popular. It's hard to see a staple mythic such as Voice go for much less than $10.
Spellskite is a versatile sideboard card. It was famous as a way to deal with Splinter-Twin, which some have been rallying to be unbanned in Modern. The argument for a Splinter-Twin unban is that Twin decks make interactive decks like Jund better, and hence improve the format and make it fairer. Right now Midrange interactive decks like Jund have been playing pretty poorly in the meta. Spellskite also answers a variety of decks such as Bogles and Infect. At $8 a piece, Spellskite is lower than it has ever been. It wouldn't be a bad idea to pick them up while they are cheap. You never know what deck it might answer in the future.