Mathew Knowles -- Hawking Old Beyonce Stuff for Top Dollar ... Deep Discounts on Solange

Beyonce's dad is trying to make ends meet by unloading tons of her souvenirs from her career in a massive garage sale -- which also features Solange stuff ... in the bargain bin.

As we've told you ... Mathew Knowles is having baby mama troubles -- which might explain why he started selling off some Bey treasures outside his office in Houston last Friday.

As of Monday, there were plenty of items available ... including a giant Beyonce poster for $200, old tour books for $20, and various pieces of House of Dereon clothing. On a budget? You can find a Solange CD for $1.96.

In the non-Beyonce aisle -- Mathew's also selling office furniture ... so, it looks like a total fire sale.

We're told Mathew shunned an attempt to haggle the oversized Beyonce poster down to $145 ... standing firm at two hundy.