Hello there, and welcome to SRP!
For a really tight budget, there is Larry at Whipped Dog, he sells a "sight unseen" razor for $43 and a "flawed sight unseen" for$28, but apart from that there is only a lucky find at an antique shop or in an auction, both would require some hands on love before use (and might not work at all, in a worst case scenario. I would not recommend this route). Not an easy feat to find a useable straight for that little money. Larry does sell double edge razors for as little as $16 I see, so perhaps that is your best bet on your current budget.

Best of luck!