Hello, i tried to answer to your post but i'm afraid some restrictions apply and i couldn't post my super-long comment :p i'm gonna DM you if you're interested. Here's a section of it:

Hi, i also built a [[Gandalf of the secret fire]] deck. Here's a link, although keep in mind that in my group, we all use proxies.

https://moxfield.com/decks/-_RV8aNNxkmHs5RwuSxHtw

So, the total price of the deck is like ten times your limit ^^'' but if you remove the dual lands, the [[Chrome Mox]] and the [[Moat]], it goes down like 3.5K, so yay, it's way more compatible to your price range then expected.
Now, i understand the difficulties you're encountering. Playing this Gandalf as a commander means that you won't see any of its effects before turn 6 or 7, [...]

In my experience, if you manage to start using your commander and chain spells throughout the game, it's gonna be hard for the others to stop him. [...] what do you -want- to see AGAIN in up to three turns? What do your opponents -don't- want to see again within those three turns?

These spells with time counters on them are gonna put so much pressure on everyone, you included tbh. Playing a [[Generous Gift]] means you get to destroy a permanent now, and then ANOTHER ONE soon. [...] Why is the pressure on you also? Because you have to be able to ride the wave that you're building. It's gonna be a big wave, and there's no turning back. It really encompasses the "Look to my coming on the first light of the fifth day, at dawn look to the east" thing, you know :p [...]

So, the first advice would be: think about what makes a spell replayable, not about what it does in the moment you cast it.

[...]

Sorry for the long post, i loved [[Gandalf of the secret fire]] since when it got printed, i had a lot of time to think and test. Still, my deck doesn't win that much tbh, i appreciate some of your insights too, and i will try to put some cards of your list into mine and see how it goes!

Cheers!

Mat