looking to upgrade my macbook pro late 2014 storage

being a song writer/DJ 250GB is really not enough for me. The amount of money i paid for it I'm really disapointed it didn't come with more i was expecting at least 512GB. Apple have told me they don't do upgrades and i wouldn't feel conftable doing it my self as my laptop is my pride and joy.

How ever apple did say that PC world might do it for me, Im looking 1TB storage will it be expensive i am willing to settle for at least 500gb no less.

Here is some specs from my system any help would be really appreciated????

MacBook Pro: (Retina, 15-inch, Mid 2014)

Processer: 2.2 GHz Intel Core i7

Memory: 16 GB 1600 MHz DDR3

Graphics: Intel Iris Pro 1536 MB

251 GB Flash Storage

Capacity: 251 GB (251,000,193,024 bytes)

Model: APPLE SSD SM0256F

Revision: UXM2JA1Q

Native Command Queuing: Yes

Queue Depth: 32

Removable Media: No

Detachable Drive: No

BSD Name: disk0

Medium Type: Solid State

TRIM Support: Yes

Partition Map Type: GPT (GUID Partition Table)

S.M.A.R.T. status: Verified

Capacity: 250.14 GB (250,140,434,432 bytes)

BSD Name: disk0s2

Content: Apple_CoreStorage

PS Also my current storage is SSD right flash is SSD????

BSD Name: disk0

Medium Type: Solid State

TRIM Support: Ye

S.M.A.R.T. status: Verified

Removable Media: No

Detachable Drive: No

Removable Media: No

Detachable Drive: No

Removable Media: No

Detachable Drive: No