Cheap is definitely the most common way to say that something is not expensive.
e.g.
Is there a good and cheap restaurant nearby?
Wow! This cake is so cheap!
People can say something is "a steal" when it's price is much lower than usual. We use "a steal" because it seems so cheap that it feels like you are stealing the item when you buy it!
e.g.
You have to buy this guitar, it's a steal!
A good/great deal is also very commonly said when something is sold for a lower price than usual.
e.g.
I bought 5 kg of potatoes for only 40 yen. What a great deal!
cheapとは、高価ではないものに対してよく使う単語です。
例：
Is there a good and cheap restaurant nearby?
この近くに、おいしくて安いレストランはありますか？
Wow! This cake is so cheap!
わぁこのケーキすごく安い！
"a steal" とは、価格がいつもより安いときに使うフレーズです。"a steal" は、価格が安すぎて、買うときに盗んでいるような気分になってしまいそうです。
例：
You have to buy this guitar, it's a steal!
このギター買ったほうがいいよ！ものすごく安い！
A good/great deal もまた、いつもより安い価格で売っている物に対してよく使う言葉です。
例：
I bought 5 kg of potatoes for only 40 yen. What a great deal!
5キロのじゃがいもを40円で買った。なんてお得なの！
If something isn't expensive we would say it is cheap. "I bought some cheap earrings yesterday". "Oh my gosh, look at this, it's so cheap". However, cheap can also be a negative word when we are describing something not well made or attractive. "It looks cheap and nasty".
If we have made some great cheap purchases, we would say to our friends "What a bargain". Meaning - we found some great stuff for a great price!
高価なものでないものには、cheapを使います。
"I bought some cheap earrings yesterday".
昨日安いイアリングを買ったよ。
"Oh my gosh, look at this, it's so cheap".
わぁ、これ見て。すごく安い。
しかし、cheapはきちんと作られていないものや魅力的でないものを表現するときなど、ネガティブな意味で使われることもあります。
"It looks cheap and nasty"
それ、安っぽくてひどく見える。
もしいいものを安く買ったときには、友達には、安い値段でいいものが買えたねという意味で、 "What a bargain"と言うことができます。
If something is described as "Cheap" or "it only costs a little" then you only need a little bit of money to buy it.
"Inexpensive" is the opposite word for expensive.
何かを "Cheap" （安い）や "it only costs a little"（安い）と言い表すと、それを買うのに少しのお金しかいらない、と言う意味になります。
"Inexpensive"（高価ではない） とは"expensive"（高価）の反対の言葉になります。
You may go to the shops and be dismayed at how 'expensive' items are. You may check your wallet and your bank account and your pockets to see if you have enough to pay for just one small and extremely 'expensive' item! Or, you may find something which seems incredibly 'cheap'. In fact it is so cheap you think you have discovered 'a great buy! 'A bargain' in fact!
The opposite of expensive is cheap/inexpensive. This means that it doesn't cost a lot of money maybe due to the quality or brand. However if something is good quality and you buying at a very low price you can it is a bargain.
Example sentence:
I am going to buy that bag it is very cheap.
I do not like inexpensive gifts.
expensiveの対義語は cheap/inexpensiveです。cheap/inexpensiveは、質やブランドのためにコストがかからないという意味です。しかし、質のいいものを低価格で買うときは、 bargain（お買い得）と言います。
例：
I am going to buy that bag it is very cheap.
あのかばんを買うわ。とても安いわ。
I do not like inexpensive gifts.
安っぽいギフトは好きじゃない。
As cheap as chips.' is an informal way to say that something is very cheap and not expensive.
"The curry rice was as cheap as chips."
If you wanted to say something was cheap using more formal vocabulary then you would say it was very inexpensive. For example, 'The curry rice was inexpensive.'
As cheap as chips'（非常に安い/二束三文）
これはインフォーマルな表現で何かがとても安い、高くないという意味になります。
【例】
"The curry rice was as cheap as chips."
（このカレーライスはとっても安かったです）
何かがとても安い事をフォーマルに表現したい場合は"very inexpensive"（非常に安い）を使うことが出来ます。
【例】
'The curry rice was inexpensive.'
（このカレーはとても安かったです）
This bag is so not expensive.
So not expensive?
Yeah, it is the total opposite of expensive.
So, cheap? It is cheap? Is that what you mean?
Yes, I mean it is cheap. Thanks.
I hope that helps.
Have a great day.
Will
「値段が安い」とは"The price is cheap”と言えます。
"Cheap"「安い」の反対語は"expensive"「高い」です。
関連語で"affordable"「手ごろな値段」があります。
例文："This piano would be affordable for me." 「このピアノなら私にも買える値段です。」
"Cheap things can break easily."「安いものは簡単に壊れることがある。」
「安い」を意味する単語は cheap, reasonable, inexpensive などたくさんあります。
cheap は「安い」という意味に加え、安っぽい、というニュアンスが含まれます。安かろう悪かろうといった感じで品質も悪いイメージになります。
reasonable はお得感のある「安い」になります。合理的な、という意味もありので、手頃でお値打ちというイメージになります。
inexpensive は高いという意味の expensive の否定形で、品質にかかわらず値段だけで考えて安い、というニュアンスになります。他二つと比べるとニュートラルな単語ですね。
It’s quite cheap. You should buy another one.
それは安すぎるよ。別のものを買ったほうがいい。
The lunch at the restaurant is reasonable.
そのレストランのランチはお手頃価格だ。
I’m looking for the most inexpensive route to Tokyo.
東京へ行く最も安いルートを探しています。
When something is a bargain it is very cheap and affordable. It is often used for describing a discount or a sale. It is commonly used in Australia.
-I bought 5 chocolates for the price of 2, it was a bargain!
-They have a discount on black Friday, the prices will be very low.
アメリカ合衆国 
イギリス 
南アフリカ 
ミャンマー 
オーストラリア 
日本 
