Keep in mind that (clause)

"Keep in mind" means to remember. But the word "remember" can be used in a lot of different kinds of situations. "Keep in mind" is more specific. It means to remember a fact and continue to think about it while you're making decisions.

For example, if you're planning an event for a club you belong to, you can tell the people that are helping you:

Keep in mind, our budget is pretty small.

In this case, everyone knows what the budget is, but you want them to remember that when they make suggestions for the event.

You can include "that" in this phrase or leave it out in more casual speech:

Keep in mind that you'll need to submit your application no later than Monday the 31st.

Keep in mind it's due on Monday. 

give (someone) a ballpark

A "ballpark" is a rough estimate. In other words, it's a guess about an amount that's close to the correct number, but not exact. You use it like this:

Here's an estimate of the cost. Keep in mind, it's just a ballpark.

We'll call up the electrician and have them give us a ballpark, but I'll check with you before I have them do any work.

This phrase comes from the sport of baseball. A "ball park" in a place where people watch baseball games. If two locations are within the same ball park, then they're not exactly close to each other, but they're not too far away either.

an estimate

An "estimate" is a formal guess about how much something is going to cost. You can make an estimate for things like:

• a construction project
• a software product that your company is building

Estimates are often documents which show in detail the expected costs for something. However, if someone tells you the expected price in a meeting or over the phone, that can also be called a "pricing estimate".

cost

The words "price" and "cost" are very close in meaning, but there are slight differences. "Price" emphasizes how much the seller has decided to charge for something. "Cost", on the other hand, emphasizes how much you paid for something. So you can say something like this:

The original price was $120, but it only cost me $90 because I had an employee discount.

When a professional like a lawyer, contractor, etc. offers a service, they usually talk about the "cost" rather than the "price". This makes it seem a little more like the amount was not chosen by them personally, but is just a necessary fact.