Amazon has the Silicon Power A55 M.2 2280 256GB SATA III Internal Solid State Drive (SU256GBSS3A55M28AB) for $35 with free shipping. Has excellent Amazon Reviews.
Amazon has the HP 256GB x900w USB 3.0 Flash Drive (P-FD256HP900-GE) for $30 with free shipping. Retail price: $70. Temporarily out of stock but still you purchase it.
Amazon has the Patriot Burst 2.5" 480GB SATA III Internal SSD (PBU480GS25SSDR) for $50 with free shipping. Has up to 560 MB/s read and 540 MB/s write speeds.
Has good Amazon Reviews.
Amazon has the SanDisk 128GB Cruzer USB 2.0 Flash Drive (SDCZ36-128G-B35) for $18 with free shipping on $25+ or with Prime. List price: $25. Can be used with both Mac and Windows systems. Has good Amazon Reviews.
Amazon has the SanDisk SSD PLUS 240GB Solid State Drive (SDSSDA-240G-G26) for $33 with free shipping. Retail price: $110. Features faster boot-up, shutdown, application load and response, up to 20X faster than your old hard drive, read/write speeds of up to: 530MB/s/440MBs, generous battery life, cool, quiet operation.