Trade price is good but a 100 per cent discount is better so you might want to check how to get those wins in GTA Online street races before buying a Remus.
GTA Online is giving out free cars as part of the Los Santos Tuners update but they do require some effort from the players. Namely, the first in line, Annis Remus, requires players to end in top three in the new races, three days in a row. This would be a massive challenge usually since highly skilled racers are numerous in GTAO but there are a few tricks that will make this challenge a lot easier.
First, you should focus on Street Races and ignore Pursuit Races entirely. This is because Street Races have fewer participants and therefore fewer racers that you need to beat. Ideally, the race will start with just four people in it, meaning only the last place will not get Prize Ride Challenge progress. If you're having trouble getting into a four-player race because hosts want more participants, just host the race yourself and start as soon as the fourth player joins.
To maximise your chances of winning or placing in the top three, you should pick a good car. Dinka Jester RR and Karin Calico GTF are easily the best choices for this. The first one has better handling and top speed but Calico has amazing acceleration to compensate for understeer. It also gets major boosts from bumps in the road, making you even faster.
If you don't have access to any of these two cars, just host the race yourself and disable custom vehicles. That way you can pick a stock Calico or Jester RR just like everyone else.
On top of that, if you have a friend that's willing to help you, you can just invite them into the race so they can throw it and guarantee that you place in the top three. If you don't have a friend around, you can always ask around the GTA Online Discord and finding a good samaritan shouldn't be too hard since the races only take a few minutes.