Quad Core i7 Apple MacBook Pro 15″ Inch Intel Laptop 16GB RAM 2TB Hard Drive

This MacBook Pro sells for about $700.00 currently and does not really need much when it comes to upgrades. A new battery might be a good idea and these can be had for about $50.00   and that would be the only real upgrade you would need for this MB Pro

If the 2TB of storage is too much you could sacrifice storage for speed and swap out the 2TB drive for a SSD drive in either 256GB or 512GB sizes from under $100 for a new drive.  If you need more space the 1TB drives are dropping in price and are now down to about $300.00

Assuming you did this you would  have a fast i7 MacBook Pro with 16GB of RAM and a 1TB SSD for about $1000.00

Shop for 15 inch MacBook Pro models on eBay and Amazon