dàikuān dà de tàocān bǐjiào guì.

Because in Chinese, modifiers normally come before the noun they describe.

Here, 带宽大的 is a descriptive phrase meaning something like whose bandwidth is large or with large bandwidth, and it modifies 套餐.

So the structure is:

带宽大的 + 套餐
= plans that have large bandwidth

This is a very common Chinese pattern:

[description] + 的 + noun

For example:

• 价格高的手机 = phones with high prices / expensive phones
• 速度快的网络 = networks with fast speeds

的 links a descriptive phrase to the noun it modifies.

In this sentence:

• 带宽大 = the bandwidth is large
• 带宽大的套餐 = plans for which the bandwidth is large

So 的 turns 带宽大 into something that can describe 套餐.

A useful way to think about it is:

• 带宽大 = a statement
• 带宽大的套餐 = a noun phrase

Without 的, the phrase would sound wrong here.

Chinese often uses 大 and 小 for quantities or capacities that English might describe in other ways.

So 带宽大 literally looks like bandwidth big, but it naturally means:

• high bandwidth
• large bandwidth

This is normal Chinese usage. In Chinese, 大 can describe things like:

• 声音大 = loud
• 雨大 = heavy rain
• 工作量大 = heavy workload
• 带宽大 = large/high bandwidth

So even if English uses a different adjective, Chinese may still use 大.

Here 比较 means relatively, rather, or fairly.

So:

比较贵 = relatively expensive / rather expensive

It does not mean compare in this sentence.

That is because 比较 has more than one use:

1. verb: to compare

   • 比较两个方案 = compare two plans

2. adverb: relatively / rather

   • 这个比较贵 = this is relatively expensive

In your sentence, it is the second use.

Because 比较 is already acting as the degree adverb.

In Mandarin, predicate adjectives often need some kind of degree marker in ordinary statements. So instead of just saying:

• 套餐贵

Chinese often says:

• 套餐很贵
• 套餐比较贵
• 套餐特别贵

Here, 比较 fills that role, so 很 is not needed.

Yes, you can.

Both are natural, but the nuance is different:

• 带宽大的套餐比较贵 = plans with large bandwidth are relatively / rather expensive
• 带宽大的套餐很贵 = plans with large bandwidth are expensive / very expensive

So 比较贵 sounds a bit softer or more relative, while 很贵 sounds stronger and more direct.

Because 比较 here does not introduce a specific comparison target.

• 比较贵 just means relatively expensive
• it does not explicitly say compared with what

If you want a direct comparison, you would use 比:

• 带宽大的套餐比带宽小的套餐贵。
  = Plans with larger bandwidth are more expensive than plans with smaller bandwidth.

So:

• 比较贵 = relatively expensive
• 比……贵 = more expensive than...

Yes.

The sentence structure is:

带宽大的套餐 + 比较贵

So:

• 带宽大的套餐 = the plans with large bandwidth
• 比较贵 = are relatively expensive

That means the whole noun phrase 带宽大的套餐 is functioning as the subject.

Yes, and that is also natural.

There is a small difference in nuance:

• 带宽大的套餐比较贵 = plans with large bandwidth are relatively expensive
• 带宽比较大的套餐比较贵 = plans with relatively large bandwidth are relatively expensive

In the second version, the first 比较 modifies 大, so it softens 带宽大:

• 带宽大 = bandwidth is large
• 带宽比较大 = bandwidth is relatively large

So both are correct, but the second one sounds a bit more qualified.

Yes, if the noun is clear from context.

For example:

• 带宽大的比较贵。

This means something like:

• The high-bandwidth ones are relatively expensive.

In Chinese, the head noun can be omitted when it is already understood.

套餐 originally means a set meal or combo, but in modern usage it is also very common for service plans, especially:

• phone plans
• internet plans
• data packages
• bundled service packages

So in this sentence, 套餐 means something like:

• plan
• package
• service package

The exact English translation depends on context, but in telecom or internet contexts, plan is often the best choice.

Yes. 贵 simply means expensive, and Chinese does not need to mention the actual price.

So:

• 这个套餐贵。 = This plan is expensive.
• 那个比较贵。 = That one is relatively expensive.

This works just like English. You only mention the actual price if you want to be specific.

Yes.

It sounds like a general observation:

• plans with larger bandwidth tend to be more expensive

There is no classifier, no number, and no specific determiner like 这个 or 那些, so the sentence reads naturally as a broad statement rather than talking about one particular plan.