Here is how I handled my standard door deck. It's side is also geared towards turning into a straight mill deck, however it's original form is for three-seperate win conditions.

http://tappedout.net/mtg-decks/opening-dat-door-on-ya/

Any interest in adding a Maze's End win-con to this? Of course, it vastly changes the mana-base. Makes it a lot cheaper, though. You'd just need to change out those 8 ramp spells for more wipes and fogs, perhaps.

I think I've been convinced to add 2 Urban Evolution s. I've removed two Ranger's Path to fit them in.

I also agree with upping the Supreme Verdict s to 3. -1 Cyclonic Rift for that. I might go for a 4-2 split if I see the verdicts working better than the rifts.

Maze's End is a funny card (I really should build a deck around it), but it would ruin my mana ramp as Farseek and Ranger's Path can't fetch gates.

Ral Zarek would allow you to use the door door the turn it comes into play, Also would take the target off you for a little bit because players try and figure out what to destroy first u or the planeswalker.

I know your kinda looking for budget options but honestly in a 5 color deck you really shouldn't be playing any basic land. 2-4 of each shock land (Far seek and Ranger's Path will still allow you to play them for the green shocks are still forests)

The reason why basic lands are there are twofold:
1- This isn't a 5 colour deck: it's a green/blue with a splash of white, where black and red are only needed at the very end.
2- Gatecreeper Vine wouldn't work with shock-lands and I found basics to work better than gates in this deck.

Is Temporal Mastery a good fit here?

Not really. As I have no creatures to attack with or no abilities to activate, the extra turn wouldn't allow me to do that much. All the cards I currently run in my deck are strictly better than Temporal Mastery .

Makes sense, I just remember playing against a similar deck that ran them and it opened him up to a lot of options (back to back Urban Evolution s, Door to Nothingness without a turn for me to respond, etc.). I can't remember what his specific build was tho, so I understand that it might not fit yours! Regardless, still a killer deck, +1 man :)

Doorkeeper would be good for sideboard mill, I've been thinking about making a Axebane Guardian + Doorkeeper pillowfort deck myself.

I did run 4 Doorkeeper s in the sideboard, but when Mind Grind was released, I realised that my mana ramp allowed me to cast it with X > 6 most of the time which normally results in 18-20 cards milled.
In all, this a lot faster than Doorkeeper which normally hits for 4-5 each time.

This, is the definition of fun. +1

I didn't have time to read through every comment but I don't know that I saw Alchemist's Refuge and I think it has a spot, it isn't rotation friendly but it's not expensive, and it lets you flash in your door on the end of their turn to get around having to wait a turn to win

Not a bad idea at all: I'll it out this Friday. This whole deck isn't rotation friendly, so it doesn't matter what goes in it at this time.
Once Theros is released the deck will change to Modern and receive a massive overhaul, while still maintaining the Door/Mill flavour.

Instead of Sphere of Suns I'd rather use Amulet of Vigor to help bring in those Shock Lands without the cost of 2 life. Plus your Door to Nothingness will come in untapped as well.

Amulet of Vigor seems like a nice addition.
Let's see how it plays

Couple Fabricate ?

Instead of Wall of Shards or maybe instead of Plumeveil Wall of Denial ?

The reason I put Plumeveil was to kill stuff, but you're right: probably Wall of Denial is the better option.

I toyed with the idea of Fabricate a while back, but in the end I went for 3 Sphinx's Revelation which most of the time allows me to draw Door to Nothingness anyway and has the added bonus of gaining me life.

how about Sylvan Caryatid ?

I don't want to rely too much on mana from creatures as I'll be casting quite a few Supreme Verdict s. I'd much rather have Farseek s for my two drop mana ramp.

What about Utopia Sprawl , it looks like you are relying on forests anyway so the drawback should affect you and you have a none creature based ramp effect. (I would like to play this deck in my local playgroup just for the looks...but...shock lands expensive :( )

Haunting Echoes makes a much better miller card than Jace. With just 5-10 unique cards in the graveyard, you've reduced your opponent's deck to a pile of mostly lands.

-4 Wall of Shards +4 Fog Bank