$40 (assuming USD) is a little on the low end for a full costume. You may have to alter your budget to complete the costume, or alter the costume to fit your budget.
Since this is a plain-clothes costume you can probably thrift for most of it. Thrift stores generally have a wide assortment of lost-cost clothing that works well for cosplay. Look for pieces that are fairly accurate that may require slight modification. For example, a white cardigan can work for this character if you dye it grey. You may have to check several thrift stores to find good costume pieces to use and good prices. Thrifting is only beneficial to the budget-conscious cosplayer if you can find the garments at a reduced price! If they’re almost as much as you would pay in store, it may be better to just buy from a store or online.
Another option is to buy online from places like China. The quality is usually lower and shipping can take 20+ days. However, there is usually a wide selection of items at surprisingly low prices. For example, you may be able to find similar looking running shoes for about $10.
Sometimes sewing your own garment is the cheaper option. I think you will be able to make an orange tie for cheaper than you could buy one. If you require a sewing pattern make sure to factor that into your cost to determine if sewing is the cheaper option. If a dress shirt pattern is $10 and it is only $5 to buy a shirt at a thrift store then the thrift store is going to be the better choice.
Since you have so much time you can use it to your advantage. Hold out for sales, choose longer shipping at lower costs and spread the cost of your project out so it isn’t impacting your wallet all at once!