This is simple.

Have an EXP item exclusive shop at spawn selling certain items. It could easily be located on the top level of the current starshop because there's nothing there really.

Proposed Items:
All current passive mob eggs currently obtainable through voting, for something like 3000 EXP times the level of their lucky voting tier. This puts mob eggs at:
Pig Eggs: 3000 EXP
Sheep Eggs: 6000 EXP
Ocelot & Wolf Eggs: 9000 EXP
Mooshroom Spawn Eggs: 12000 EXP

Also toss in some lame stuff from the star shop:
Wither Skeleton Skulls: 100,000 EXP
Music Discs:
Cat, 13: 500 EXP
Blocks, Chirp, Far, Mall, Mellohi, Stal, Strad, Ward, Wait: 50,000 EXP
11: 100,000 EXP if you want to make it rarer than the others like it currently is.

Also maybe some end exclusive stuff like
Enderdragon Heads, Elytra for 300,000 EXP each?

(for obvious reasons this should be paired with @a18greek18's suggestion to change the instant voting rewards).

Tinyurl: https://tinyurl.com/hjq5f89

 

How else are you gonna get em?

 

You're saying they can't be that rare, so I'm asking how exactly you're going to get them if they can't be that rare :p

 

Cat and 13 are cheap thus 500 EXP.

The others are much more difficult to obtain and I guarantee you can't buy them for $500