While not the low-cost dealer for hardware, much of Adafruit's prices reflect the significant investment in software and solutions support.
SPI based TFT 3.5 inches:
https://www.adafruit.com/product/3651
Other larger display:
https://www.buydisplay.com/4-3-tft-lcd-display-module-controller-board-serial-spi-i2c-mcu
... and a potential solution that will require some compatibility investigation:
https://www.adafruit.com/product/1590