Question about a couple sentences. "la compro"..."te espero"..
 

I am starting to come across phrases that are being said differently. Here are a few examples:

Te espero afuera.
La vende mas barata?
La compro.

I know what they all say. I am sure that the first one says "I will wait for you outside". But why is it like that and not like "voy a esperar para ti afuera" or "esperare para ti afuera"...l Why isnt the second one "puedes la vende mas barata?" And the third "la comprare".... Or another variation?

I'll wait for you outside
Esperaré por ti afuera

I wait for you outside
(yo) espero por ti afuera

I wait outside
(yo) espero afuera

¿la puedes vender más barata?
Can you sell it cheaper?

¿la vende más barata?
Do you sell it cheaper

La compro
I buy it

La compraré
I'll buy it.

You're learning three things about the Spanish present tense:
1) It can be used to convey the immediate future. So, "I'll wait for you outside" is a correct translation of the first sentence.
2) It also means:
I'm waiting for you outside.
3) And:
I wait for you outside. (I await you outside.)

The verb esperar means 'wait for'. That's why I added the 'await' sentence. You shouldn't add 'para' (or 'por', for that matter), just like we don't add a preposition to 'await'.

Direct object pronouns are found in each of your sentences. In Spanish, the DOP precedes the conjugated verb. In English, they follow it. Perhaps that's why you're trying to place the object behind the verb.

The second sentence translates as:
Do you sell it cheaper? / Are you selling it cheaper? / Will you be selling it cheaper (soon)?
Can you sell it cheaper? is a possible translation, but only if both parties are on the same wavelength. Adding poder to the mix is the same thing as asking 'Are you capable (read ability) of selling it cheaper?'

The third sentence translates into three English sentences, as well:
I'm buying it.
I buy it.
I'll buy it (soon).

Do you understand the use of the direct object pronouns in each sentence?