List of Long Duration Spells

[Bjarkmundur]

You can hire a spellcaster to cast a 1st or 2nd level spell. To get the most bang for your... coins, you should probably choose a spell that lasts for a very long time.
There are of course many shorter duration spells that can help you with specific problems, such as comprehend languages. This list focuses more on general use.
Scrolls are considered magic items. They are expensive to make, hard to find the correct scroll you need, and even harder to convince your DM to let you have. Seeing how a single hire of a spellcaster can sustain him for a month (Modest or Comfortable lifestyle), most lower level spellcasters are happy to help. At least if your cause aligns with theirs, or your deception rolls are high enough to beat their insight ;)

Concentration and Class

Not many are willing to spend hours concentrating on a spell for complete strangers, so you're almost always better off looking for spells that don't require it.
Spells are limited by class, so don't go to the Emerald Enclave looking for a wizard spell, you're not likely to find it.

1st Level Spells - 30gp:

Goodberry (Druid, Ranger)
Identify (Bard, Wizard)
Mage Armor (Sorcerer, Wizard)

2nd Level Spells - 50gp

Aid (Cleric, Paladin)
Arcane Lock (Wizard)
Continual Flame (Cleric, Wizard)
Darkvision (Druid, Ranger, Sorcerer, Wizard)
Gentle Repose (Cleric, Wizard)

Are there any other spells you can think of that might be useful?

[Contrast]

I'm not sure what criteria you're using.

Why are Identify and Augury on this list for example? Worth noting that spells with a casting time of longer than 1 action do require concentration while casting as well.

[Tanarii]

I'm not sure what criteria you're using.

Pretty sure the criteria is: spells you might pay someone to cast that benefit you long term, or right before you go do something adventure-y.

Identify because it's effectively permanent identification on your behalf.

But it puts Augury out. It only affect the caster's specified action within the next 30 minutes. It can't be cast on someone else's behalf.

Cure Wounds might be useful, if you've access to a caster and need to keep adventuring before you'll have access to a long rest.

[ff7hero]

It probably costs 100g for a casting of Continual Flame, as there's a 50g consumed Material Component.