There is/was a lot of aftermarket available for this kit. That is until AFV Club and Skybow both released superb kits of the exact same tank. I have all three of the M41 Walker Bulldog kits and just about all aftermarket that was made for the Tamiya kit. Don't waste the money on the various AM sets for the Tamiya kit, one or two items will cost as much as one of the better kits.

Since you are short on funds, I'll give a reader's digest version of some items that can be improved with little or no expense.
1. Blank off the undersides of the sponson boxes (underside of fender boxes) with simple sheet styrene.
2. Notice in the box art that the sides of the center sponson boxes have X shaped strengthening imprints. Using the box art and top of the sponson box relief as a guide, carefully scribe the X with a sharp knife or other scribing instrument. Once you have the X groove, use a source of heat to stretch some sprue to fit into the groove. Cut to size and use liquid cement to attach.

3. The forward sponson boxes just have a series of vertical strengthening ribs, use the same techique to add them as well. (Box art shows tank with turret over rear)

4. Blank off the motorization holes on the underside of the lower hull and around the final drive housing of the drive sprocket. Also on the sides of the hull are some holes that need to be filled. Place the interior bulkhead first.

5. The outer sprocket half should have 4 lightening holes in them, but the recess is too shallow to add them. The compensating idler wheel should also have lightening holes in the rim (see box art), but only add them if you think you can do it and make them look even (I'd omit this too).

6. I'd consider replacing the tool rack with something from the parts box. Same deal with the 5 gal. cans and the .50 cal machine gun.

7. To detail out the driver's vision blocks, I'd fill the gap with something simple like Elmer's white glue and paint the face gloss black when dry.

8. The actual headlight guards are flat pieces of metal welded together, you can carefully sand them down to a more appropriate scale thickness or you can find some scrape pieces of photoetch fret to cut to size and replicate.

9. One thing I would consider spending some money on would be replacement tracks. I'm not talking about high-priced individual links, but AFV Club makes a set of vinyl tracks #AF 35052 that run about $7-8. The kit tracks have no detail on the inner surface except for a token center guide (guide teeth). Also if you put out a want ad on various model forums, someone may have a set of the vinyl tracks that came with their AFV Club kit that they subsequently replaced with the AFV Club single link tracks. Those are #AF 35046 and run about $14-15 a set.